i18n: include jinja file encoding in babel.ini

* Currently when you run `python setup.py extract_messages` it will Not include *.jinja template files.
This one will fix that.

babel.ini

@@ -2,6 +2,7 @@
 #
 # Copyright (C) 2019 CERN.
 # Copyright (C) 2019 Northwestern University.
+# Copyright (C) 2024 KTH Royal Institute of Technology.
 #
 # Invenio-RDM-Records is free software; you can redistribute it and/or modify it
 # under the terms of the MIT License; see LICENSE file for more details.
@@ -16,6 +17,9 @@ encoding = utf-8
 [jinja2: **/templates/**.html]
 encoding = utf-8
 
+[jinja2: **/templates/**.jinja]
+encoding = utf-8
+
 # Extraction from JavaScript files
 
 [javascript: **.js]