Use the correct action input parameter

pr-checks/checks/with-checkout-path.yml

@@ -1,6 +1,10 @@
 name: "Use a custom `checkout_path`"
 description: "Checks that a custom `checkout_path` will find the proper commit_oid"
 steps:
+  # This ensures we don't accidentally use the original checkout for any part of the test.
+  - name: Delete original checkout
+    run: |
+      rm -rf .
   # Check out the actions repo again, but at a different location.
   # choose an arbitrary SHA so that we can later test that the commit_oid is not from main
   - uses: actions/checkout@v4
@@ -12,7 +16,7 @@ steps:
       tools: ${{ steps.prepare-test.outputs.tools-url }}
       # it's enough to test one compiled language and one interpreted language
       languages: csharp,javascript
-      source-path: x/y/z/some-path/tests/multi-language-repo
+      source-root: x/y/z/some-path/tests/multi-language-repo
       debug: true
   - name: Build code (non-windows)
     shell: bash