Upgrade to Gradle 6.8

Closes gh-26368

gradle/ide.gradle

@@ -55,14 +55,6 @@ eclipse.classpath.file.whenMerged { classpath ->
 	}
 }
 
-// Ensure that test fixture dependencies are handled properly in Gradle 6.7.
-// Bug fixed in Gradle 6.8: https://github.com/gradle/gradle/issues/14932 
-eclipse.classpath.file.whenMerged {
-	entries.findAll { it instanceof ProjectDependency }.each {
-		it.entryAttributes.remove('without_test_code')
-	}
-}
-
 // Ensure that JMH sources and resources are treated as test classpath entries
 // so that they can see test fixtures.
 // https://github.com/melix/jmh-gradle-plugin/issues/157

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.8-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists