Update actions/cache@v2 -> v4

doc/industrial_ci_action.yml

@@ -29,7 +29,7 @@ jobs:
       CCACHE_DIR: "${{ github.workspace }}/.ccache" # directory for ccache (and how we enable ccache in industrial_ci)
     steps:
       - uses: actions/checkout@v4 # clone target repository
-      - uses: actions/cache@v2 # fetch/store the directory used by ccache before/after the ci run
+      - uses: actions/cache@v4 # fetch/store the directory used by ccache before/after the ci run
         with:
           path: ${{ env.CCACHE_DIR }}
           # This configuration will always create a new ccache cache starting off from the previous one (if any).