LUCENE-9650: disable errorprone on jdk16+ (#2171)

gradle/testing/alternative-jdk-support.gradle

@@ -34,6 +34,7 @@ JavaInstallation altJvm = {
 
 // Set up root project's property.
 rootProject.ext.runtimeJava = altJvm
+rootProject.ext.runtimeJavaVersion = altJvm.javaVersion
 
 if (!currentJvm.javaExecutable.equals(altJvm.javaExecutable)) {
   // Set up java toolchain tasks to use the alternative Java.

gradle/validation/error-prone.gradle

@@ -15,6 +15,12 @@
  * limitations under the License.
  */
 
+// LUCENE-9650: Errorprone on master/gradle no longer works with JDK-16
+if (rootProject.runtimeJavaVersion > JavaVersion.VERSION_15) {
+  logger.warn("WARNING: errorprone disabled (won't work with JDK ${rootProject.runtimeJavaVersion})")
+  return
+}
+
 allprojects { prj ->
   plugins.withType(JavaPlugin) {
     prj.apply plugin: 'net.ltgt.errorprone'