Various CI fixes including using pull request trigger

We are doing this because push is very bad choice of trigger for CI on github PRs.
 Example: guardian/mobile-apps-api#2760

 Co-authored-Roberto Tyley

.github/workflows/testonpush.yml → .github/workflows/ci.yml

@@ -1,9 +1,13 @@
-name: Test on push
-
+name: CI
 on:
+  workflow_dispatch:
+  pull_request:
+
+  # triggering CI default branch improves caching
+  # see https://docs.github.com/en/free-pro-team@latest/actions/guides/caching-dependencies-to-speed-up-workflows#restrictions-for-accessing-a-cache
   push:
-    branches: [ "**" ]
-  workflow_dispatch: {}
+    branches:
+      - main
 
 jobs:
   test:
@@ -15,10 +19,10 @@ jobs:
       pull-requests: write
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Setup JDK
-        uses: actions/setup-java@v3
+        uses: actions/setup-java@v4
         with:
           distribution: corretto
           java-version: 11