updated to v4 in .github/workflows

.github/workflows/pull_request_ci.yml

@@ -25,7 +25,7 @@ jobs:
     steps:
       # First, we check out the repository's code using the Github Actions' "Checkout" tool.
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: 'recursive'
 
@@ -59,7 +59,7 @@ jobs:
             sudo chown root:root /usr/bin/tar && sudo chmod u+s /usr/bin/tar
       - name: Cache protobuf-c
         id: cache-protobuf-c
-        uses: actions/cache@v3 # Uses the Github Actions' "Cache" tool
+        uses: actions/cache@v4 # Uses the Github Actions' "Cache" tool
         with:
           # These are the files we cache
           path: |