test(tool/cmd/migrate): add test to fetchGoogleapisWithCommit

[zhumin8]

Add test to fetchGoogleapisWithCommit. For #4514 (comment)

[gemini-code-assist]

Code Review

This pull request refactors fetchGoogleapisWithCommit to accept fetch.Endpoints as a parameter, which makes the function testable. A new test, TestFetchGoogleapisWithCommit, is added, effectively mocking the GitHub API using httptest. The changes are well-implemented, and the new test adheres to the project's testing guidelines. I have one suggestion to improve the maintainability of the new test by replacing a hardcoded repository path with the variable used in the implementation.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.90%. Comparing base (c4d97d7) to head (2e2b5c4).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
tool/cmd/migrate/legacylibrarian.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4550      +/-   ##
==========================================
+ Coverage   79.65%   79.90%   +0.24%     
==========================================
  Files         109      109              
  Lines        9126     9115      -11     
==========================================
+ Hits         7269     7283      +14     
+ Misses       1346     1322      -24     
+ Partials      511      510       -1     

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