Fix F009, F010, F012: Remove fast loader assertions for Python 3.9
Update three tests that were failing due to assertions about Python <3.9
fast loader behavior. Since the string-project fixture was updated to
Python 3.9 in F007, these tests now run with Python 3.9+ which uses the
fast loader directly without falling back to the slow loader.
Changes:
- test_predict_takes_string_inputs_and_returns_strings_to_stdout (F012):
Remove assertions for fast loader fallback messages at lines 31-32
- test_predict_writes_strings_to_files (F009):
Remove assertions for fast loader fallback messages at lines 159-160
- test_predict_runs_an_existing_image (F010):
Remove assertions for fast loader fallback messages at lines 183-184
All three tests now assert that the fallback message should NOT be
present, which is the correct behavior for Python 3.9+.
