ci: test both push and pull_request events

I think we have a bug with pull_request events so...

action.yml

@@ -75,9 +75,12 @@ runs:
 
         # If we were triggered by a PR then this is easy
         if [ "$GITHUB_EVENT_NAME" = "pull_request" ]; then
-                log "Triggered by a pull request with index: $GITHUB_HEAD_REF"
+                # shellcheck disable=SC2016
-                log "Expected PR URL: $GITHUB_SERVER_URL/$GITHUB_REPOSITORY/pulls/$GITHUB_HEAD_REF"
+                # expanded by the runner
-                echo "pr-number=$GITHUB_HEAD_REF" >> "$GIHUB_OUTPUT"
+                pr_number='${{ github.event.number }}'
+                log "Triggered by a pull request with index: $pr_number"
+                log "Expected PR URL: $GITHUB_SERVER_URL/$GITHUB_REPOSITORY/pulls/$pr_number"
+                echo "pr-number=$pr_number" >> "$GIHUB_OUTPUT"
                 exit 0
         fi
 
@@ -91,6 +94,8 @@ runs:
                 -H "Authorization: token $GITHUB_TOKEN" \
                 -H 'Accept: application/json')
 
+        log "Open PRs: $(echo "$prs" | jq --compact output 'map(.number)')"
+
         pr_number=$(echo "$prs" |
                 jq --arg head_ref "$head_ref" '.[] | select(.head.ref == $head_ref) | .number')