ci: Bump github action version

Fix warning:
"The following actions uses node12 which is deprecated and will be forced
to run on node16: actions/checkout@v2."

.github/workflows/ci-linux.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Install deps
       run: sudo apt-get install check ninja-build doxygen