Cache Maven repo during GitHub Actions

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1886257 13f79535-47bb-0310-9956-ffa450edef68

.github/workflows/test-maven.yml

     - name: Cache
       uses: actions/cache@v2.1.3
       with:
-        # A list of files, directories, and wildcard patterns to cache and restore
-        path: lib
-        # An explicit key for restoring and saving the cache
-        key: poi-third-party-libs
+        path: ~/.m2/repository
+        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+        restore-keys: |
+          ${{ runner.os }}-maven-
 
     - name: Build with Maven
       run: (cd sonar && mvn -B validate package --file pom.xml)