Check legacy headers when streaming headers

[gBillal]

If the option legacy_headers_as_lists is set to true and running the following code will return an error

Req.get!("https://github.com/wojtekmach/req/archive/refs/tags/v0.5.5.zip", into: File.stream!("test.tar.tz"))

** (BadMapError) expected a map, got: []
    (stdlib 5.2.1) :maps.merge([], %{"cache-control" => ["max-age=0, private"], "content-length" => ["0"], "content-security-policy" => ["default-src 'none'; base-uri 'self'; child-src github.com/assets-cdn/worker/ github.com/webpack/ github.com/assets/ gist.github.com/assets-cdn/worker/; connect-src 'self' uploads.github.com www.githubstatus.com collector.github.com raw.githubusercontent.com api.github.com github-cloud.s3.amazonaws.com github-production-repository-file-5c1aeb.s3.amazonaws.com github-production-upload-manifest-file-7fdce7.s3.amazonaws.com github-production-user-asset-6210df.s3.amazonaws.com *.rel.tunnels.api.visualstudio.com wss://*.rel.tunnels.api.visualstudio.com objects-origin.githubusercontent.com copilot-proxy.githubusercontent.com proxy.individual.githubcopilot.com proxy.business.githubcopilot.com proxy.enterprise.githubcopilot.com *.actions.githubusercontent.com wss://*.actions.githubusercontent.com productionresultssa0.blob.core.windows.net/ productionresultssa1.blob.core.windows.net/ productionresultssa2.blob.core.windows.net/ productionresultssa3.blob.core.windows.net/ productionresultssa4.blob.core.windows.net/ productionresultssa5.blob.core.windows.net/ productionresultssa6.blob.core.windows.net/ productionresultssa7.blob.core.windows.net/ productionresultssa8.blob.core.windows.net/ productionresultssa9.blob.core.windows.net/ productionresultssa10.blob.core.windows.net/ productionresultssa11.blob.core.windows.net/ productionresultssa12.blob.core.windows.net/ productionresultssa13.blob.core.windows.net/ productionresultssa14.blob.core.windows.net/ productionresultssa15.blob.core.windows.net/ productionresultssa16.blob.core.windows.net/ productionresultssa17.blob.core.windows.net/ productionresultssa18.blob.core.windows.net/ productionresultssa19.blob.core.windows.net/ github-production-repository-image-32fea6.s3.amazonaws.com github-production-release-asset-2e65be.s3.amazonaws.com insights.github.com wss://alive.github.com api.githubcopilot.com api.individual.githubcopilot.com api.business.githubcopilot.com api.enterprise.githubcopilot.com; font-src github.githubassets.com; form-action 'self' github.com gist.github.com copilot-workspace.githubnext.com objects-origin.githubusercontent.com; frame-ancestors 'none'; frame-src viewscreen.githubusercontent.com notebooks.githubusercontent.com; img-src 'self' data: blob: github.githubassets.com media.githubusercontent.com camo.githubusercontent.com identicons.github.com avatars.githubusercontent.com private-avatars.githubusercontent.com github-cloud.s3.amazonaws.com objects.githubusercontent.com secured-user-images.githubusercontent.com/ user-images.githubusercontent.com/ private-user-images.githubusercontent.com opengraph.githubassets.com github-production-user-asset-6210df.s3.amazonaws.com customer-stories-feed.github.com spotlights-feed.github.com objects-origin.githubusercontent.com *.githubusercontent.com; manifest-src 'self'; media-src github.com user-images.githubusercontent.com/ secured-user-images.githubusercontent.com/ private-user-images.githubusercontent.com github-production-user-asset-6210df.s3.amazonaws.com gist.github.com; script-src github.githubassets.com; style-src 'unsafe-inline' github.githubassets.com; upgrade-insecure-requests; worker-src github.com/assets-cdn/worker/ github.com/webpack/ github.com/assets/ gist.github.com/assets-cdn/worker/"], "content-type" => ["text/html; charset=utf-8"], "date" => ["Sat, 26 Oct 2024 19:45:23 GMT"], "location" => ["https://codeload.github.com/wojtekmach/req/zip/refs/tags/v0.5.5"], "referrer-policy" => ["no-referrer-when-downgrade"], "server" => ["GitHub.com"], "strict-transport-security" => ["max-age=31536000; includeSubdomains; preload"], "vary" => ["X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, Accept-Encoding, Accept, X-Requested-With"], "x-content-type-options" => ["nosniff"], "x-frame-options" => ["deny"], "x-github-request-id" => ["D9C2:3264D4:92D3045:962FC6F:671D46D2"], "x-xss-protection" => ["0"]})
    (req 0.5.6) lib/req/finch.ex:140: anonymous fn/2 in Req.Finch.finch_stream_into_collectable/5
    (elixir 1.15.4) lib/map.ex:916: Map.update!/3
    (req 0.5.6) lib/req/finch.ex:140: anonymous fn/3 in Req.Finch.finch_stream_into_collectable/5
    (finch 0.19.0) lib/finch.ex:376: anonymous fn/3 in Finch.stream/5
    (finch 0.19.0) lib/finch/http1/conn.ex:324: Finch.HTTP1.Conn.receive_response/8
    (finch 0.19.0) lib/finch/http1/conn.ex:131: Finch.HTTP1.Conn.request/8
    (finch 0.19.0) lib/finch/http1/pool.ex:60: anonymous fn/10 in Finch.HTTP1.Pool.request/6

In this PR, we address the issue by calling Req.Response.put_header/3 to add the headers instead of converting them into a map.