MINOR: Upgrade Gradle to 6.6 (#9160)

A couple of important bug fixes affecting Scala compilation are the main driver:
* https://github.com/gradle/gradle/issues/13224
* https://github.com/gradle/gradle/issues/13392

Full release notes for the other improvements:
* https://docs.gradle.org/6.6/release-notes.html

Reviewers: Manikumar Reddy <manikumar.reddy@gmail.com>

gradle/dependencies.gradle

@@ -61,7 +61,7 @@ versions += [
   bcpkix: "1.66",
   checkstyle: "8.20",
   commonsCli: "1.4",
-  gradle: "6.5",
+  gradle: "6.6",
   gradleVersionsPlugin: "0.29.0",
   grgit: "4.0.2",
   httpclient: "4.5.12",

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.6-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

gradlew

@@ -84,7 +84,7 @@ esac
 # Loop in case we encounter an error.
 for attempt in 1 2 3; do
   if [ ! -e $APP_HOME/gradle/wrapper/gradle-wrapper.jar ]; then
-    if ! curl -s -S --retry 3 -L -o "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" "https://raw.githubusercontent.com/gradle/gradle/v6.5.0/gradle/wrapper/gradle-wrapper.jar"; then
+    if ! curl -s -S --retry 3 -L -o "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" "https://raw.githubusercontent.com/gradle/gradle/v6.6.0/gradle/wrapper/gradle-wrapper.jar"; then
       rm -f "$APP_HOME/gradle/wrapper/gradle-wrapper.jar"
       # Pause for a bit before looping in case the server throttled us.
       sleep 5