Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/java.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
     - name: Set up JDK 1.8
       uses: actions/setup-java@master
       with:

.github/workflows/publish.yml

@@ -12,7 +12,7 @@ jobs:
     if: contains(github.event.head_commit.message, '[ci skip]') == false
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Generate build number
       id: buildnumber
       uses: WalshyDev/build-number@master