Pin actions/checkout's own workflows to a known, good, stable version. (#1776)

* Pin actions/checkout's own workflows to a known, good, stable version.

* fixed failing unit test

* fix unit test

.github/workflows/update-main-version.yml

@@ -22,7 +22,7 @@ jobs:
     # Note this update workflow can also be used as a rollback tool.
     # For that reason, it's best to pin `actions/checkout` to a known, stable version
     # (typically, about two releases back).
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v4.1.6
       with:
         fetch-depth: 0
     - name: Git config