TypeError: send_file() got an unexpected keyword argument 'attachment_filename'

[igushev-truesource]

Old code start throwing this exception:
TypeError: send_file() got an unexpected keyword argument 'attachment_filename'

[davidism]

As called out in the changelog:

Remove previously deprecated code. #4667

Old names for some send_file parameters have been removed. download_name replaces attachment_filename, max_age replaces cache_timeout, and etag replaces add_etags. Additionally, path replaces filename in send_from_directory.

These have been raising deprecation warnings since 2.0. Be sure to run your tests with warnings treated as errors so you can respond to deprecations (in any library, not just Flask).