chore(conventional-commits-workflow): get PR title from env var (#553)

Follows advice at https://docs.github.com/en/actions/security-guides/security-hardening-for-github-actions#using-an-intermediate-environment-variable

.github/workflows/conventional-commits.yml

@@ -20,11 +20,13 @@ jobs:
         # verb: feat, fix, ...
         # scope: refers to the part of code being changed.  E.g. " (accounts)" or " (accounts,canisters)"
         # !: Indicates that the PR contains a breaking change.
-      - run: |
-          if [[ "${{ github.event.pull_request.title }}" =~ ^(feat|fix|chore|build|ci|docs|style|refactor|perf|test)(\([-a-zA-Z0-9,]+\))?\!?\: ]]; then
+      - env:
+          TITLE: ${{ github.event.pull_request.title }}
+        run: |
+          echo "PR title: $TITLE"
+          if [[ "$TITLE" =~ ^(feat|fix|chore|build|ci|docs|style|refactor|perf|test)(\([-a-zA-Z0-9,]+\))?\!?\: ]]; then
               echo pass
           else
               echo "PR title does not match conventions"
-              echo "PR title: ${{ github.event.pull_request.title }}"
               exit 1
           fi