Bump checkout action to v4

.github/workflows/CompileTest.yml

@@ -88,7 +88,7 @@ jobs:
       # First of all, we clone the repo using the "checkout" action.
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       # Finally, we compile the sketches, using the FQBN that was set in the boards matrix.
       - name: Compile examples for ${{ matrix.config.board }}