Update CI workflow to use Java 17 & 21

Maven plugins used in the build now require Java 17. We still target
Java 11 for our output.

Also update the actions used to the latest version.

.github/workflows/build.yml

@@ -8,14 +8,14 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [11, 17]
+        java: [17, 21]
     name: build with jdk ${{matrix.java}}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         name: checkout
 
-      - uses: actions/setup-java@v3
+      - uses: actions/setup-java@v4
         name: set up jdk ${{matrix.java}}
         with:
           java-version: ${{matrix.java}}