Update to setup-java v2, and use adopt builds

https://github.com/actions/setup-java/blob/main/docs/switching-to-v2.md

PiperOrigin-RevId: 384750269

Author: cushon

.github/workflows/ci.yml

@@ -60,9 +60,10 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-maven-
       - name: 'Set up JDK ${{ matrix.java }}'
-        uses: actions/setup-java@v1
+        uses: actions/setup-java@v2
         with:
           java-version: ${{ matrix.java }}
+          distribution: 'adopt'
       - name: 'Install'
         shell: bash
         run: mvn install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
@@ -86,9 +87,10 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-maven-
       - name: 'Set up JDK 15'
-        uses: actions/setup-java@v1
+        uses: actions/setup-java@v2
         with:
           java-version: 15
+          distribution: 'adopt'
           server-id: sonatype-nexus-snapshots
           server-username: CI_DEPLOY_USERNAME
           server-password: CI_DEPLOY_PASSWORD