HSEARCH-4072 Add cache to GH workflow

Signed-off-by: Yoann Rodière <yoann@hibernate.org>

.github/workflows/contributor-build.yml

@@ -31,6 +31,18 @@ jobs:
         uses: actions/setup-java@v1
         with:
           java-version: 11
+      - name: Get year/month for cache key
+        id: get-date
+        run: |
+          echo "::set-output name=yearmonth::$(/bin/date -u "+%Y-%m")"
+        shell: bash
+      - name: Cache Maven local repository
+        uses: actions/cache@v2
+        id: cache-maven
+        with:
+          path: ~/.m2/repository
+          # refresh cache every month to avoid unlimited growth
+          key: maven-localrepo-${{ steps.get-date.outputs.yearmonth }}
       - name: Set up Maven
         run: ./mvnw -v
       - name: Build and test
@@ -41,3 +53,5 @@ jobs:
         with:
           name: test-reports-java11
           path: './**/*-reports/'
+      - name: Omit produced artifacts from build cache
+        run: rm -r ~/.m2/repository/org/hibernate/search