fix: csv recognition by consumer

paperless-ngx detects the file format via the mime-type based on the response of python-magic which rely on the response of the file command.
In version 5.39 (which is shipped with debian bullseye and I think many more non-rolling distributions) of the file command a *.csv will be detected as "application/csv" instead of "text/csv" as in newer versions.

src/paperless_text/signals.py

@@ -11,5 +11,6 @@ def text_consumer_declaration(sender, **kwargs):
         "mime_types": {
             "text/plain": ".txt",
             "text/csv": ".csv",
+            "application/csv": ".csv",
         },
     }