Remove migueleliasweb/go-github-mock

[JoannaaKL]

Summary

Remove migueleliasweb/go-github-mock and use testify for mocks

Why

Fixes #1492

MCP impact

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

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)

[Copilot]

Pull request overview

This PR removes the migueleliasweb/go-github-mock dependency and replaces it with an in-house HTTP handler-map based mocking approach using testify for assertions. The change simplifies the testing infrastructure while maintaining all existing test functionality.

Key Changes:

• Removed go-github-mock and its transitive dependencies (gorilla/mux, golang.org/x/time/rate)
• Introduced new mocking infrastructure using HTTP handler maps (MockHTTPClientWithHandlers)
• Updated all test files to use the new mocking approach
• Updated license files and documentation to reflect dependency removals

Reviewed changes

Copilot reviewed 19 out of 20 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
go.mod / go.sum	Removed migueleliasweb/go-github-mock and transitive dependencies (gorilla/mux, go-github/v71, golang.org/x/time)
third-party/**/LICENSE	Removed license files for removed dependencies
third-party-licenses.*.md	Updated to remove references to removed dependencies
pkg/github/mock_shim_test.go	New file implementing compatibility shim for legacy test patterns with handler-map based mocking
pkg/github/helper_test.go	Added endpoint constants for Projects V2 API, renamed testify/mock import to avoid collision
pkg/raw/raw_mock.go	Changed endpoint patterns from structs to string constants
pkg/github/*_test.go	Updated all test files to use new MockHTTPClientWithHandlers approach
docs/testing.md	Updated testing documentation to reference new HTTP handler-map helpers
.github/copilot-instructions.md	Updated instructions to document new mocking approach