🔧(backend) allow text/x-tex mimetype

The text/x-tex mimetype is used by .tex files containing LaTeX document.
The application/x-tex is already allowed but we also have to allow this
mimetype otherwise some document with the .tex extension can't be
uploaded.

src/backend/drive/settings.py

@@ -765,6 +765,7 @@ class Base(Configuration):
             "text/vtt",
             "text/x-c",
             "text/x-python",
+            "text/x-tex",
             "text/x-vcard",
             "video/3gpp",
             "video/3gpp2",