Fixed #22972 -- HashedFilesMixin.patterns should limit URL matches to their respective filetypes

Please see https://code.djangoproject.com/ticket/22972 for context.
I think the hardcoded hash should be replaced by `relpath = self.hashed_file_path("...")`
There was a recent change (adding end of file newlines to the CSS flies) that caused the hash of all files to change so this would allow us not to have to update this hash each time.