Update Gradle wrapper to 6.5 (#57580)

* Update Gradle wrapper to 6.5
* Fix groovy incompatibility issue after gradle update
* Fix Gstring String incompatibility

buildSrc/src/main/resources/minimumGradleVersion

@@ -1 +1 @@
-6.4.1
+6.5

distribution/bwc/build.gradle

@@ -107,7 +107,7 @@ BuildParams.bwcVersions.forPreviousUnreleased { BwcVersions.UnreleasedVersionInf
     task checkoutBwcBranch() {
       dependsOn fetchLatest
       doLast {
-        String refspec = System.getProperty("bwc.refspec.${bwcBranch}") ?: System.getProperty("tests.bwc.refspec.${bwcBranch}") ?: "${remote}/${bwcBranch}"
+        def refspec = System.getProperty("bwc.refspec." + bwcBranch) ?: System.getProperty("tests.bwc.refspec." + bwcBranch) ?: "${remote}/${bwcBranch}"
         if (System.getProperty("bwc.checkout.align") != null) {
           /*
               We use a time based approach to make the bwc versions built deterministic and compatible with the current hash.

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.4.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionSha256Sum=3fd824892df8ad5847be6e4fb7d3600068437de172939fd657cc280a1a629f63
+distributionSha256Sum=c9910513d0eed63cd8f5c7fec4cb4a05731144770104a0871234a4edc3ba3cef