- Use copy task that branches for 8.3 and above to avoid using project.exec in a dolast block. 

part 1/n for flutter/flutter/issues/138523 

This PR does not test the 8.3 branch but instead builds the ability to write a branching gradle test. 
After fixing this project.exec action there I discovered a second that needs to be removed or migrated in order for the build to work. 

Related reading https://docs.gradle.org/8.0/userguide/configuration_cache.html#config_cache:requirements
https://docs.gradle.org/current/javadoc/org/gradle/process/ExecOperations.html (not used but considered) 
https://docs.gradle.org/8.2/dsl/org.gradle.api.tasks.Copy.html#org.gradle.api.tasks.Copy:fileMode