build: only lint version numbers for pull requests

Fixes: #39850

PR-URL: #40027
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

.github/workflows/linters.yml

@@ -53,7 +53,7 @@ jobs:
       - name: Environment Information
         run: npx envinfo
       - name: Get release version numbers
-        if: ${{ github.event.pull_request.base.ref == github.event.pull_request.base.repo.default_branch }}
+        if: ${{ github.event.pull_request && github.event.pull_request.base.ref == github.event.pull_request.base.repo.default_branch }}
         id: get-released-versions
         run: ./tools/node-lint-md-cli-rollup/src/list-released-versions-from-changelogs.mjs
       - name: Lint docs