Continue replacing migueleliasweb/go-github-mock

[JoannaaKL]

Summary

Why

Fixes #

What changed

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Prompts tested (tool changes only)

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)

[JoannaaKL]

@copilot analyse existing changes and remove github.com/migueleliasweb/go-github-mock in pkg/github/repositories_test.go and in pkg/github/issues_test.go

[Copilot]

@JoannaaKL I've opened a new pull request, #1654, to work on those changes. Once the pull request is ready, I'll request review from you.