Add ccache to github actions

.github/workflows/sitl_tests.yml

@@ -20,8 +20,21 @@ jobs:
       run: wget https://github.com/mavlink/MAVSDK/releases/download/v0.24.0/mavsdk_0.24.0_ubuntu18.04_amd64.deb
     - name: Install MAVSDK
       run: dpkg -i mavsdk_0.24.0_ubuntu18.04_amd64.deb
+    - uses: actions/cache@v1.1.0
+      id: ccache-persistence
+      with:
+        path: ~/.ccache
+        key: ccache-sitl-tests
+        restore-keys: |
+          ccache-sitl-tests
+    - name: setup ccache
+      run: mkdir -p ~/.ccache && echo "max_size = 1G" > ~/.ccache/ccache.conf && ccache -z && ccache -s
     - name: Build PX4 in SITL integration test mode
       run: DONT_RUN=1 make px4_sitl PX4_CMAKE_BUILD_TYPE=Coverage gazebo mavsdk_tests
+    - name: ccache post-run
+      run: ccache -s && ccache -z
+
+      # Run mavsdk tests
     - name: Run multicopter simulation test
       run:  test/mavsdk_tests/mavsdk_test_runner.py --model iris --speed-factor 20 --iterations 1 --fail-early
     - name: Run multicopter with optical flow simulation test