matrix-synapse.plugins.matrix-synapse-s3-storage-provider: add missing dependency (#256485)

this is required for the s3_media_upload script to work

pkgs/servers/matrix-synapse/plugins/s3-storage-provider.nix

···
 , pythonOlder
 , tqdm
 , twisted
+, psycopg2
 }:
 
 buildPythonPackage rec {
···
     humanize
     tqdm
     twisted
+    psycopg2
   ]
   # For the s3_media_upload script
   ++ matrix-synapse-unwrapped.propagatedBuildInputs;