[actions] Cache maven depenencies

https://github.com/actions/cache

Author: harawata

.github/workflows/ci.yaml

@@ -1,5 +1,5 @@
 #
-#    Copyright 2009-2020 the original author or authors.
+#    Copyright 2009-2021 the original author or authors.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");
 #    you may not use this file except in compliance with the License.
@@ -35,5 +35,12 @@ jobs:
         uses: actions/setup-java@v1
         with:
           java-version: ${{ matrix.java }}
+      - name: Cache local Maven repository
+        uses: actions/cache@v2
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-
       - name: Test with Maven
         run: ./mvnw test -B -D"license.skip=true"