GitHub: Use checkout@v2

Fixes security concerns of v1

Change-Id: I1fb72c3845611db239f6bed79b4768a7ceadccc8
Reviewed-by: Cristian Adam <[email protected]>

.github/workflows/build_cmake.yml

@@ -35,7 +35,7 @@ jobs:
           }
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
 
     - name: Download Ninja and CMake
       shell: cmake -P {0}