Use maven cache for java setup.

Author: camporter

.github/workflows/maven.yml

@@ -18,5 +18,6 @@ jobs:
         with:
           distribution: 'temurin'
           java-version: ${{matrix.java}}
+          cache: 'maven'
       - name: Build with Maven
         run: mvn verify -B -e -V --file pom.xml -Dgpg.skip=true