Add missing import for mask_sig in bandcamp.py

[zliebersbach]

Fix the following issue when an error is thrown in self._request:

date	stream	content
2023/10/16 16:03:23	stdout	NameError: name 'mask_sig' is not defined
2023/10/16 16:03:23	stdout	^^^^^^^^
2023/10/16 16:03:23	stdout	raise BandcampError(f'Failed to make HTTP request to {mask_sig(url)}: {e}') from e
2023/10/16 16:03:23	stdout	File "/usr/local/lib/python3.11/dist-packages/bandcampsync/bandcamp.py", line 89, in _request
2023/10/16 16:03:23	stdout	^^^^^^^^^^^^^^^^^^^^^^^^^
2023/10/16 16:03:23	stdout	soup = self._request('get', url)
2023/10/16 16:03:23	stdout	File "/usr/local/lib/python3.11/dist-packages/bandcampsync/bandcamp.py", line 147, in verify_authentication
2023/10/16 16:03:23	stdout	bandcamp.verify_authentication()
2023/10/16 16:03:23	stdout	File "/usr/local/lib/python3.11/dist-packages/bandcampsync/init.py", line 19, in do_sync
2023/10/16 16:03:23	stdout	do_sync(cookies_path, cookies, dir_path, media_format_env, temp_dir)
2023/10/16 16:03:23	stdout	File "/usr/local/bin/bandcampsync-service", line 74, in

[meeb]

Ah, thanks! I think I need to go and kick my linter...