Use %F field code in .desktop entry

On Linux, the `%u` field code results in multiple Dangerzone instances
being launched when opening multiple documents with Dangerzone from
e.g. Nautilus, as `%u` signifies that the application (in this case -
Dangerzone) can only open a single file/URL at once.

This changes the field code to `%F` as Dangerzone (now) supports
converting multiple files at once. We use `%F` (multiple local files)
instead of `%U` (multiple files and/or URLs) since Dangerzone does not
support opening URLs.

See also the Desktop Entry Specification [1] for more information on the
field codes.

Fixes #797

[1]: https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s07.html

CHANGELOG.md

@@ -17,6 +17,7 @@ since 0.4.1, and this project adheres to [Semantic Versioning](https://semver.or
 
 - Make OCR work again in Qubes Fedora 38 templates ([issue #737](https://github.com/freedomofpress/dangerzone/issues/737))
 - Make .svg / .bmp files selectable when browsing files via the Dangerzone GUI ([#722](https://github.com/freedomofpress/dangerzone/pull/722))
+- Linux: Allow opening multiple files at once, when selecting them from the user's file manager ([issue #797](https://github.com/freedomofpress/dangerzone/issues/797))
 
 ### Changed
 

install/linux/press.freedom.dangerzone.desktop

@@ -2,7 +2,7 @@
 Name=Dangerzone
 GenericName=Dangerzone
 Comment=Take potentially dangerous PDFs, office documents, or images and convert them to a safe PDF
-Exec=dangerzone %u
+Exec=dangerzone %F
 Terminal=false
 Type=Application
 Icon=press.freedom.dangerzone