Add support for Python 3.13

Bump our max supported Python version to 3.13, now that PySide6 supports
it.

Fixes #992

install/linux/dangerzone.spec

@@ -216,17 +216,6 @@ convert the documents within a secure sandbox.
 %prep
 %autosetup -p1 -n dangerzone-%{version}
 
-# XXX: Bump the Python requirement in pyproject.toml from <3.13 to <3.14. Fedora
-# 41 comes with Python 3.13 installed, but our pyproject.toml does not support
-# it because PySide6 in PyPI works with Python 3.12 or earlier.
-#
-# This hack sidesteps this issue, and we haven't noticed any paticular problem
-# with the package that is built from that.
-%if 0%{?fedora} == 41
-sed -i 's/<3.13/<3.14/' pyproject.toml
-%endif
-
-
 %generate_buildrequires
 %pyproject_buildrequires -R