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}}