chore: Add a "validate actions" script to validate workflow/action YAML in CI - W-24800910

.github/workflows/validateActions.yml

@@ -0,0 +1,19 @@
+name: Validate actions
+
+on: pull_request
+
+permissions:
+  contents: read
+
+jobs:
+  validate-actions:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+          cache: npm
+      - run: npm ci
+      - run: npm run check:actions
+      - run: npm run test:actions

CONTRIBUTING.md

@@ -21,6 +21,7 @@ Agreement. You can do so by going to https://cla.salesforce.com/sign-cla.
 
 ## Pull Requests
 
+- Run `npm ci`, then `npm run check:actions` (Node.js 24+) to validate workflow/action YAML and reusable-workflow inputs. Self-references, including `salesforcecli/github-workflows/...@main`, are checked against this checkout. Run `npm run test:actions` for validator regression tests. Both checks run on PRs.
 - Develop features and bug fixes in _topic_ branches off main, or forks.
 - _Topic_ branches can live in forks (external contributors) or within this repository (internal contributors).
   - When creating _topic_ branches in this repository please prefix with `<initials>/`. For example: `mb/refactor-tests`.