Update actions/checkout action to v5 (#58)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
     - name: Checkout repo under /prebid-server-java-docker-image
-      uses: actions/checkout@v4
+      uses: actions/checkout@v5
       with:
         fetch-depth: '0'
         path: prebid-server-java-docker-image
@@ -41,7 +41,7 @@ jobs:
 
     - name: Checkout prebid-server-java under /prebid
       if: '!env.TAG_ALREADY_EXISTS'
-      uses: actions/checkout@v4
+      uses: actions/checkout@v5
       with:
         repository: 'prebid/prebid-server-java'
         ref: ${{ env.TARGET_TAG }}