fix: Groovy 3.0.20 compatibility (#1779)

Author: matrei

build.gradle

@@ -39,14 +39,14 @@ apply plugin: 'project-report'
 allprojects {
     repositories {
         mavenCentral()
-        maven { url "https://repo.grails.org/grails/core" }
+        maven { url = 'https://repo.grails.org/grails/core' }
         if(isSnapshot) {
-            maven { url "https://repo.grails.org/grails/libs-snapshots-local" }
+            maven { url = 'https://repo.grails.org/grails/libs-snapshots-local' }
         }
         if(groovyVersion && groovyVersion.endsWith('-SNAPSHOT')) {
             maven {
-                name 'JFrog OSS snapshot repo'
-                url 'https://oss.jfrog.org/oss-snapshot-local/'
+                name = 'JFrog Groovy snapshot repo'
+                url = 'https://groovy.jfrog.io/artifactory/libs-snapshot-local'
             }
         }
     }

grails-datastore-gorm-rx/src/main/groovy/org/grails/datastore/rx/collection/RxPersistentSet.groovy

@@ -104,7 +104,7 @@ class RxPersistentSet extends PersistentSet implements RxPersistentCollection, R
     @Override
     List<Serializable> getAssociationKeys() {
         if(keys != null) {
-            return keys.toList()
+            return keys.toList() as List<Serializable>
         }
         else {
             return Collections.emptyList()

grails-datastore-gorm-rx/src/main/groovy/org/grails/datastore/rx/collection/RxPersistentSortedSet.groovy

@@ -131,7 +131,7 @@ class RxPersistentSortedSet extends PersistentSet implements SortedSet, RxPersis
     @Override
     List<Serializable> getAssociationKeys() {
         if(keys != null) {
-            return keys.toList()
+            return keys.toList() as List<Serializable>
         }
         else {
             return Collections.emptyList()