Use repo initial branch in GitCore PR fetch integration test

- Return `initialBranch` from test repo setup helper
- Replace hardcoded `main` checkout/push/assertions with detected branch name
fb4f9aa58eJulius Marminge committed on 3/10/2026, 5:50:45 AM· committed by Julius Marmingeparentde21f4d
1 file changedLine totals unavailable