ci: disable arch

```
 #11 0.137 --2025-09-18 10:41:06--  https://aur.archlinux.org/cgit/aur.git/snapshot/libstrophe-git.tar.gz
```

This currently blocks us at #2066.

Author: jubalh

.github/workflows/main.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        flavor: [arch, debian, fedora, ubuntu]
+        flavor: [debian, fedora, ubuntu]
 
     name: Linux
     steps: