Bump go-httpbin

[mstoykov]

What?

Bump go-httpbin to v2

Why?

There is a low CVE that is unlikely to be relevant as go-httpbin is only used for tests.

But while a lot of the usages are different echo endpoints, there are some that aren't so removing this seems very unliekly.

On the other hand go-httpbin has no external dependancies and while the update adds a bunch of lines, it doesn't seem excessive.

Checklist

• [ ] I have performed a self-review of my code.
• [ ] I have commented on my code, particularly in hard-to-understand areas.
• [ ] I have added tests for my changes.
• [ ] I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• [ ] I have added the correct milestone and labels to the PR.
• [ ] I have updated the release notes: link
• [ ] I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• [ ] I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

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