refactor: replace deprecated AbstractGlobalExtension with IGlobalExtension

- Refactor code to implement the `IGlobalExtension` interface, replacing the deprecated `AbstractGlobalExtension` class.

Author: matrei

grails-gorm-testing-support/src/main/groovy/org/grails/testing/gorm/spock/GormTestingSupportExtension.groovy

@@ -2,11 +2,11 @@ package org.grails.testing.gorm.spock
 
 import grails.testing.gorm.DataTest
 import groovy.transform.CompileStatic
-import org.spockframework.runtime.extension.AbstractGlobalExtension
+import org.spockframework.runtime.extension.IGlobalExtension
 import org.spockframework.runtime.model.SpecInfo
 
 @CompileStatic
-class GormTestingSupportExtension extends AbstractGlobalExtension {
+class GormTestingSupportExtension implements IGlobalExtension {
 
     DataTestSetupSpecInterceptor dataTestSetupSpecInterceptor = new DataTestSetupSpecInterceptor()
     DataTestSetupInterceptor dataTestSetupInterceptor = new DataTestSetupInterceptor()