pmb ci: error on using --all with script names

You can either say you want all scripts, or give a list of script names,
not both. Add it this way and not with an add_mutually_exclusive_group,
as I'll add a add_mutually_exclusive_group in the next patch to only
specify --all or --fast, but having --fast with script names is fine.

Reviewed-by: Luca Weiss <luca@z3ntu.xyz>
Link: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3C20221111072354.3431-2-ollieparanoid@postmarketos.org%3E

pmb/helpers/frontend.py

@@ -643,6 +643,9 @@ def ci(args):
 
     scripts_selected = {}
     if args.scripts:
+        if args.all:
+            raise RuntimeError("Combining --all with script names doesn't"
+                               " make sense")
         for script in args.scripts:
             if script not in scripts_available:
                 logging.error(f"ERROR: script '{script}' not found in git"