ci: test both push and pull_request events

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

action.yml

@@ -73,6 +73,17 @@ runs:
       run: |
         . "$GITHUB_ACTION_PATH/utils.sh"
 
+        # If we were triggered by a PR then this is easy
+        if [ "$GITHUB_EVENT_NAME" = "pull_request" ]; then
+                # shellcheck disable=SC2016
+                # expanded by the runner
+                pr_number='${{ 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" >> "$GIHUB_OUTPUT"
+                exit 0
+        fi
+
         log 'Determine head_ref'
         # For push & tag events it'll bet GITHUB_REF_NAME, for pull_request events it'll be GITHUB_HEAD_REF
         head_ref=${GITHUB_REF_NAME:-$GITHUB_HEAD_REF}
@@ -83,6 +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')