test: Use t.Context() instead of context.Background()

[alexandear]

This PR replaces context.Background() with t.Context() in tests. T.Context has been available since Go 1.24.

Additionally, it enables the usetesting linter to automatically suggest using t.Context() in future PRs.

The PR also modifies the helper function createRandomTestRepository by adding a *testing.T parameter. This simplifies integration tests that rely on this function.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.11%. Comparing base (b7f068f) to head (64801d6).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3750 +/- ##
=======================================
Coverage 91.11% 91.11% =======================================
Files 187 187 Lines 16702 16702 =======================================
Hits 15218 15218 Misses 1296 1296 Partials 188 188 

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[gmlewis]

Thank you, @alexandear!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell

[gmlewis]

Thank you, @zyfy29!
Merging.