mkosi: Use rawhide tools tree in CI

To build rawhide images we might need more recent tools from rawhide
itself. While Arch would generally be up-to-date enough as well, it
doesn't provide the selinux tools so we use Fedora Rawhide instead.

(cherry picked from commit 948bca0)

Author: DaanDeMeyer

.github/workflows/mkosi.yml

@@ -154,6 +154,7 @@ jobs:
           UseSubvolumes=yes
           ToolsTree=default
           ToolsTreeDistribution=fedora
+          ToolsTreeRelease=rawhide
 
           WorkspaceDirectory=$TMPDIR
           PackageCacheDirectory=$TMPDIR/cache