Migrate pkg/repoutil tests to testify assertions

[Copilot]

pkg/repoutil/repoutil_test.go used only the standard testing package with manual error checks and value comparisons. Migrated to testify for consistent assertion style and clearer failure messages.

Changes

• Imports: Added testify/assert and testify/require
• Error assertions: Replaced if err == nil/!= nil { t.Errorf(...) } with require.Error/require.NoError
• Value assertions: Replaced manual field comparisons with assert.Equal including descriptive messages
• TestSplitRepoSlug_Whitespace: Added expectedOwner/expectedRepo fields to the test table — previously the function discarded the returned values entirely
• TestSplitRepoSlug_Idempotent: Refactored bare loop into t.Run subtests with testify assertions

Before:

if err == nil {
    t.Errorf("SplitRepoSlug(%q) expected error, got nil", tt.slug)
}
if owner != tt.expectedOwner {
    t.Errorf("SplitRepoSlug(%q) owner = %q; want %q", tt.slug, owner, tt.expectedOwner)
}

After:

require.Error(t, err, "SplitRepoSlug(%q) should return an error", tt.slug)
// ...
require.NoError(t, err, "SplitRepoSlug(%q) should not return an error", tt.slug)
assert.Equal(t, tt.expectedOwner, owner, "SplitRepoSlug(%q) owner mismatch", tt.slug)

[Copilot]

Pull request overview

This PR migrates pkg/repoutil unit tests to use testify assertions for more consistent style and clearer failure output.

Changes:

• Switched from manual if err != nil / t.Errorf checks to require.NoError / require.Error.
• Replaced manual field comparisons with assert.Equal and improved failure messages.
• Updated whitespace and idempotency tests to assert returned owner/repo values and to use subtests.

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