depsync: Download .mod file from the proxy

[codebien]

Download the go.mod file from the official proxy. In this way we can support any kind of formatted version. e.g. When a specific version pinned by commit is used.

Description

Fixes # (issue)

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make test) and all tests pass.
• I have run relevant integration test locally (make integration-xxx for affected packages)
• I have run relevant e2e test locally (make e2e-xxx for disruptors, or cluster related changes)
• Any dependent changes have been merged and published in downstream modules
  

[roobre]

Hey @codebien, thanks for this PR!

If I understand this correctly, this would allow fetching to work when the version specified in go.mod is a pseudoversion e.g. v2.1.4-0.20211119122758-180fcef48034+incompatible. Am I correct?

If so this looks awesome to me so far.

[codebien]

@roobre yes, exactly. I would use the k6 master which means go.k6.io/k6 v0.46.1-0.20230921075448-d1c5ee8fb28d but using the GitHub URL didn't work, so I switched to the proxy so it can resolve any version supported by go mod command.