CI needs Java 11 to be able to upgrade to gradle 7.x

This is related to !1089 (merged). Currently, the CI fails because it provides and older version of Java.

Here is the exact error:

> Failed to apply plugin 'com.android.internal.library'.
   > Android Gradle plugin requires Java 11 to run. You are currently using Java 1.8.
     You can try some of the following options:
       - changing the IDE settings.
       - changing the JAVA_HOME environment variable.
       - changing `org.gradle.java.home` in `gradle.properties`.

I ran in that error on my machine and had to add a JAVA_HOME env var pointing to the jre provided by Android Studio.