Refactor google-java-format CI

Only test with 15 on windows and macos

PiperOrigin-RevId: 349787620

Author: cushon

.github/workflows/ci.yml

@@ -22,9 +22,23 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        os: [ ubuntu-latest ]
         java: [ 15, 11 ]
+        experimental: [ false ]
+        include:
+          # Only test on macos and windows with a single recent JDK to avoid a
+          # combinatorial explosion of test configurations.
+          - os: macos-latest
+            java: 15
+            experimental: false
+          - os: windows-latest
+            java: 15
+            experimental: false
+          - os: ubuntu-latest
+            java: 16-ea
+            experimental: true
     runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental }}
     steps:
       - name: 'Check out repository'
         uses: actions/checkout@v2
@@ -46,31 +60,6 @@ jobs:
         shell: bash
         run: mvn test -B
 
-  early_access:
-    name: 'JDK Early-Access'
-    continue-on-error: true
-    runs-on: ubuntu-latest
-    steps:
-      - name: 'Check out repository'
-        uses: actions/checkout@v2
-      - 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: 'Set up JDK ${{ matrix.java }}'
-        uses: actions/setup-java@v1
-        with:
-          java-version: 16-ea
-      - name: 'Install'
-        shell: bash
-        run: mvn install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
-      - name: 'Test'
-        shell: bash
-        run: mvn test -B
-
   publish_snapshot:
     name: 'Publish snapshot'
     needs: test