Add CI check that cmd- is not in linux keymaps + check other mods (#32334)

Motivation for the `cmd-` check is that there were a couple keybindings
using `cmd-` in the linux keymap and so these were bound to super /
windows

Release Notes:

- N/A

.github/workflows/ci.yml

@@ -183,6 +183,9 @@ jobs:
       - name: Check for todo! and FIXME comments
         run: script/check-todos
 
+      - name: Check modifier use in keymaps
+        run: script/check-keymaps
+
       - name: Run style checks
         uses: ./.github/actions/check_style