ci: Allow flatpak jobs to fail

They have been a bit flaky lately, especially the arm64 job.

.gitlab-ci.yml

@@ -109,6 +109,7 @@ package:deb-pureos-byzantium:arm64:
 flatpak@x86_64:
   stage: package
   extends: ['.flatpak@x86_64', '.vars-devel']
+  allow_failure: true
   except:
     variables:
       - $PKG_ONLY == "1"
@@ -117,6 +118,7 @@ flatpak@x86_64:
 flatpak@aarch64:
   stage: package
   extends: ['.flatpak@aarch64', '.vars-devel']
+  allow_failure: true
   except:
     variables:
       - $PKG_ONLY == "1"