Actions test.yml - add Windows CI

[MSP-Greg]

Adds Windows CI, including mswin build.

This will fail unless #162 is merged, or the test failing in ruby CI is fixed:

    1) Failure:
  TestNetHTTPS#test_session_reuse_but_expire [D:/a/ruby/ruby/src/test/net/http/test_https.rb:184]:
  <false> expected but was
  <true>.

[MSP-Greg]

Just rebased and squashed the two commits to one.

[hsbt]

Can you rebase this from HEAD?

[MSP-Greg]

@hsbt

Sorry AFK earlier

Closing, see https://github.com/ruby/net-http/pull/181