[SORMAS-Foundation#3730] actions cache for mvn packages

Author: JonasCir

.github/workflows/ci.yml

@@ -22,6 +22,12 @@ jobs:
         uses: actions/setup-java@v1
         with:
           java-version: ${{ matrix.java }}
+      - name: Cache Maven packages
+        uses: actions/cache@v2
+        with:
+          path: ~/.m2
+          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+          restore-keys: ${{ runner.os }}-m2
       - name: Build with Maven
         run: |
           cd sormas-base