(#1) Attempting to fix an issue where commitlint couldn't validate th…

…e commit messages because the PR branch was checked out as a detached head.

The error we received is below:

  error running commitlint
  fatal: ambiguous argument '46bb5821095a7e8e1ffd48f4697eec3c593c9b24^1..46bb582': unknown revision or path not in the working tree.

This was solved using a solution reported here: actions/checkout#124 (comment)

.github/workflows/validate-pr.yml

@@ -11,9 +11,12 @@ jobs:
     steps:
       - name: Check out Git repository
         uses: actions/checkout@v2
-        # We don't just checkout the last commit, but all commits
-        # This is so the commitlint GitHub Action below can lint commit messages
         with:
+          # Checkout the PR branch to avoid detached heads as seems to break the commitlint action
+          # See: https://github.com/actions/checkout/issues/124#issuecomment-586664611
+          ref: ${{ github.event.pull_request.head.ref }}
+          # We don't just checkout the last commit, but all commits
+          # This is so the commitlint GitHub Action below can lint commit messages
           fetch-depth: 0
 
       - name: Set up Node.js