Add validation for platform strings to exclude_parser.py

[jiekang]

Fixes: #5650

[jiekang]

@smlambert Would appreciate your thoughts here on the approach before I exit Draft.

And maybe I need to update the GH actions somewhere to fail when this exits with code 1?
And are there other things I can validate while I'm here?

[sophia-guo]

Alternative of global ERROR_FOUND ( needed for all log.error) to fail the github check is adding custom handler.

class ErrorTrackingHandler(logging.Handler):
    def __init__(self):
        super().__init__()
        self.error_logged = False

    def emit(self, record):
        if record.levelno >= logging.ERROR:
            self.error_logged = True

LOG = logging.getLogger("my_custom_logger")
...

# Add the custom error-tracking handler
error_tracker = ErrorTrackingHandler()
LOG.addHandler(error_tracker)

...
# Check if any ERROR or higher-level messages were logged
if error_tracker.error_logged:
    print("Errors were logged, exiting with error.")
    sys.exit(1)