GH-2097 - Upgrade GitHub actions checkout action to v4.

Author: odrotbohm

.github/workflows/build.yaml

@@ -14,7 +14,7 @@ jobs:
     steps:
 
     - name: Check out sources
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up JDK 17
       uses: actions/setup-java@v3

.github/workflows/docs.yaml

@@ -14,7 +14,7 @@ jobs:
     steps:
 
     - name: Check out sources
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up JDK 17
       uses: actions/setup-java@v3

.github/workflows/milestone.yaml

@@ -12,7 +12,7 @@ jobs:
     steps:
 
     - name: Check out sources
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up JDK 17
       uses: actions/setup-java@v3

.github/workflows/release.yaml

@@ -12,7 +12,7 @@ jobs:
     steps:
 
     - name: Check out sources
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Set up JDK 17
       uses: actions/setup-java@v3