Fixed copy and paste error

.github/workflows/gradle.yml

@@ -19,10 +19,10 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
-    - name: Set up JDK 1.8
+    - name: Set up JDK ${{ matrix.java }}
       uses: actions/setup-java@v1
       with:
-        java-version: 1.8
+        java-version: ${{ matrix.java }}
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew
     - uses: actions/cache@v2