ci: fail fast in test-each-commit script

Pass `--failfast` to the functional test runner in `.github/ci-test-each-commit-exec.py`.
Stop after the first failure to surface the root cause sooner and keep logs readable when testing ancestor commits.

Co-authored-by: MarcoFalke <*~=`'#}+{/-|&$^_@721217.xyz>

.github/ci-test-each-commit-exec.py

@@ -62,6 +62,7 @@ def main():
         f"./{build_dir}/test/functional/test_runner.py",
         "-j",
         str(num_procs * 2),
+        "--failfast",
         "--combinedlogslen=99999999",
     ])