Run some automatic tests with GitHub Actions (#68)

faster_whisper/utils.py

@@ -2,7 +2,7 @@ def format_timestamp(
     seconds: float,
     always_include_hours: bool = False,
     decimal_marker: str = ".",
-):
+) -> str:
     assert seconds >= 0, "non-negative timestamp expected"
     milliseconds = round(seconds * 1000.0)