ci: fall back on checking last 5 commit messages, instead of 20

This will allow CI status to recover faster when a bad commit message
is accidentally merged. In some cases (eg force pushes of PRs with
more than 5 commits) not all commit messages will be checked at all
times.

.github/workflows/linux.yml

@@ -109,7 +109,7 @@ jobs:
       # related: https://stackoverflow.com/questions/64708371/how-to-run-github-workflow-on-every-commit-of-a-push
       env:
         BEFORE: ${{ github.event.before }}
-        NUM:    20
+        NUM:    5
       shell: bash
       run: |
         RANGE=${BEFORE:-origin/master}..${GITHUB_HEAD_REF:+origin/$GITHUB_HEAD_REF}

.github/workflows/mac.yml

@@ -66,7 +66,7 @@ jobs:
       # related: https://stackoverflow.com/questions/64708371/how-to-run-github-workflow-on-every-commit-of-a-push
       env:
         BEFORE: ${{ github.event.before }}
-        NUM:    20
+        NUM:    5
       shell: bash
       run: |
         RANGE=${BEFORE:-origin/master}..${GITHUB_HEAD_REF:+origin/$GITHUB_HEAD_REF}

.github/workflows/push.yml

@@ -77,7 +77,7 @@ jobs:
       # related: https://stackoverflow.com/questions/64708371/how-to-run-github-workflow-on-every-commit-of-a-push
       env:
         BEFORE: ${{ github.event.before }}
-        NUM:    20
+        NUM:    5
       shell: bash
       run: |
         RANGE=${BEFORE:-origin/master}..${GITHUB_HEAD_REF:+origin/$GITHUB_HEAD_REF}

.github/workflows/windows.yml

@@ -59,7 +59,7 @@ jobs:
       # related: https://stackoverflow.com/questions/64708371/how-to-run-github-workflow-on-every-commit-of-a-push
       env:
         BEFORE: ${{ github.event.before }}
-        NUM:    20
+        NUM:    5
       shell: bash
       run: |
         RANGE=${BEFORE:-origin/master}..${GITHUB_HEAD_REF:+origin/$GITHUB_HEAD_REF}