Switch OpenJDK distribution to Zulu for GitHub Actions (#1060)

* Using TCK Tested JDK builds of OpenJDK

The AdoptOpenJDK has been discontinued since July 2021 (https://adoptopenjdk.net). Switching the distribution to Azul Zulu. When using Zulu you get all the latest updated (TCK Tested) builds for all versions of OpenJDK.

.github/workflows/main.yml

@@ -11,10 +11,7 @@ jobs:
   build:
     strategy:
       matrix:
-        java-version:
-          - 8
-          - 11
-          - 12
+        java-version: [ 8, 11, 12 ]
     runs-on: ubuntu-latest
 
     steps:
@@ -24,7 +21,7 @@ jobs:
 
       - uses: actions/setup-java@v2
         with:
-          distribution: adopt
+          distribution: zulu
           java-version: ${{ matrix.java-version }}
 
       - name: Cache Gradle packages