Adjust BWC candidates in retention lease BWC tests (#40562)

We test BWC with nodes older than 6.7.0 since such nodes would not
understand retention lease sync requests. However, we do not need to
test compatbility with nodes on or after 6.7.0 since we know these nodes
understand retention lease sync requests, which are already exercised in
other tests. Therefore, we can skip these versions when running the BWC
tests and only test against versions that do not understand retention
lease sync requests.

Author: jasontedor

qa/retention-lease-bwc/build.gradle

@@ -30,7 +30,7 @@ esplugin {
 integTest.enabled = false
 
 task bwcTest {
-  description = 'runs retention lease backwards compatability tests'
+  description = 'runs retention lease backwards compatibility tests'
   group = 'verification'
 }
 
@@ -39,6 +39,10 @@ for (Version version : bwcVersions.wireCompatible) {
     // versions before 6.5.0 do not support soft deletes
     continue
   }
+  if (version.onOrAfter("6.7.0")) {
+    // we are known to be compatible with these versions
+    continue
+  }
 
   final String baseName = "v${version}"