Update on: param for upgrade test

It was left { on: push } previously; should be { on: pull_request } and
workflow_dispatch, like the others.

Leaving for later the work of making this parameterized.

Author: reidmv

.github/workflows/test-upgrade.yaml

@@ -1,35 +1,11 @@
 ---
 name: "Upgrade test"
 
-on: push
-
-# on:
-#   workflow_dispatch:
-#     inputs:
-#       image:
-#         description: 'GCP image for test cluster'
-#         required: true
-#         default: 'centos-7'
-#       architecture:
-#         description: 'PE architecture to test'
-#         required: true
-#         default: 'standard'
-#       version:
-#         description: 'PE version to install'
-#         required: true
-#         default: '2019.8.7'
-#       version_to_upgrade:
-#         description: 'PE version to upgrade'
-#         required: true
-#         default: '2021.2.0'
-#       download_mode:
-#         description: 'peadm download_mode'
-#         required: false
-#         default: 'direct'
-#       ssh-debugging:
-#         description: 'Boolean; whether or not to pause for ssh debugging'
-#         required: true
-#         default: 'false'
+on:
+  pull_request:
+    branches: [main]
+    types: [review_requested]
+  workflow_dispatch: {}
 
 env:
   HONEYCOMB_WRITEKEY: 7f3c63a70eecc61d635917de46bea4e6