[CI] update GHA checkout action to v4

Author: jgarzik

.github/workflows/TestingCI.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Build
       run: cargo build --release --verbose
     - name: Run tests