ci: enable CI on all pushes except merge queue

Every push really should have CI. The only reason we didn't was to avoid
duplicating CI for the merge queue; looks like there's a better way to do that.

This uses
https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onpushbranchestagsbranches-ignoretags-ignore
to ignore merge queue branches.

Test plan: check that opening a github PR with this change triggers
CI, but that CI is labelled as "push" CI, then check that after merge, 
the merge queue doesn't duplicate CI, and gerrit's branches trigger CI
without a PR.

Change-Id: Id2d8bdb0b670d6906576878884844dbb64d8eb16

.github/workflows/applications.yml

@@ -18,8 +18,10 @@ on:
       eventlog:
         description: link with -eventlog
         default: 'False'
-  pull_request:
   merge_group:
+  push:
+    branches-ignore:
+      - 'gh-readonly-queue/**'
 
 env:
   AWS_ACCESS_KEY_ID: ${{ secrets.kadena_cabal_cache_aws_access_key_id }}