Tests: bl_keymap_validate failure wasn't causing tests to fail

bl_keymap_validate wasn't exiting with a non-zero exit code
on failure since [0] which unintentionally removed the assignment.

[0]: 167c4c6962

tests/python/bl_keymap_validate.py

@@ -330,6 +330,7 @@ def main() -> None:
                     print(error_text_consistency)
                 if error_text_duplicates:
                     print(error_text_duplicates)
+                has_error = True
             else:
                 print("OK!")