fix case in which if no source PKGBUILDs were updated, an exception will occur

tests/ahriman/core/build_tools/test_sources.py

@@ -264,7 +264,7 @@ def test_commit(sources: Sources, mocker: MockerFixture) -> None:
     commit_message = "Commit message"
     sources.commit(local, commit_message=commit_message)
     check_output_mock.assert_called_once_with(
-        "git", "commit", "--all", "--message", commit_message,
+        "git", "commit", "--allow-empty", "--message", commit_message,
         exception=None, cwd=local, logger=pytest.helpers.anyvar(int)
     )
 
@@ -278,7 +278,7 @@ def test_commit_autogenerated(sources: Sources, mocker: MockerFixture) -> None:
     local = Path("local")
     sources.commit(Path("local"))
     check_output_mock.assert_called_once_with(
-        "git", "commit", "--all", "--message", pytest.helpers.anyvar(str, strict=True),
+        "git", "commit", "--allow-empty", "--message", pytest.helpers.anyvar(str, strict=True),
         exception=None, cwd=local, logger=pytest.helpers.anyvar(int)
     )