Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/javadocs.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Clean up folder
       run: rm -rf Slimefun4/