LUCENE-9122: upgrade gradle wrapper to 6.0.1. Relax JVM requirement to require at least Java 11. We can't even check for higher bound because gradle itself breaks before it can execute the check script. I verified locally and it works with 11-13.

gradle/validation/check-environment.gradle

@@ -5,8 +5,8 @@ import org.gradle.util.GradleVersion
 
 configure(rootProject) {
   ext {
-    expectedGradleVersion = '5.6.4'
-    expectedJavaVersion = JavaVersion.VERSION_11
+    expectedGradleVersion = '6.0.1'
+    minJavaVersion = JavaVersion.VERSION_11
   }
 
   wrapper {
@@ -15,8 +15,8 @@ configure(rootProject) {
   }
 
   def currentJavaVersion = JavaVersion.current()
-  if (currentJavaVersion < expectedJavaVersion) {
-    throw new GradleException("Java version ${expectedJavaVersion} is required: this Java is ${currentJavaVersion} "
+  if (currentJavaVersion < minJavaVersion) {
+    throw new GradleException("At least Java ${minJavaVersion} is required, you are running Java ${currentJavaVersion} "
       + "[${System.getProperty('java.vm.name')} ${System.getProperty('java.vm.version')}]")
   }
 

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.4-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0.1-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists