Small fixes for Qubes PRM

This commit fixes 3 small issues with the way we produce our Qubes RPM:

1. The `.exists()` method follows symlinks by default, whereas we want
   to check if a symlink exists. This functionality has been added in
   Python
   3.12.

   Instead of checking if a symlink exists and then removing it, simply
   remove it and don't throw an error if it doesn't exist in the first
   place.

2. The `dz.Convert*` policies were not installed with the executable bit
   set, therefore the qube could not start.

3. The `dz.ConvertDev` policy in particular had an ambiguous shebang,
   thus we change it to explicitly call Python3

install/linux/build-rpm.py

@@ -59,8 +59,7 @@ def build(qubes=False):
     shutil.copy2(specfile_path, build_dir / "SPECS")
     rpm_dir = build_dir / "RPMS" / "x86_64"
     srpm_dir = build_dir / "SRPMS"
-    if srpm_dir.exists():
-        os.unlink(srpm_dir)
+    srpm_dir.unlink(missing_ok=True)
     os.symlink(dist_path, rpm_dir)
     os.symlink(dist_path, srpm_dir)
 

install/linux/dangerzone.spec

@@ -268,7 +268,7 @@ install -m 644 share/* %{buildroot}/usr/share/dangerzone
 # /etc/qubes-rpc.
 %if 0%{?_qubes}
 install -m 755 -d %{buildroot}/etc/qubes-rpc
-install -m 644 qubes/* %{buildroot}/etc/qubes-rpc
+install -m 755 qubes/* %{buildroot}/etc/qubes-rpc
 %endif
 
 # The following files are included in the top level of the Python source

qubes/dz.ConvertDev

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import asyncio
 import glob