[RESULT][VOTE] change default branch of grails-core to 8.0.x

[James Fredley]

The vote has passed with six +1 binding votes plus 1 additional +1.
Vote thread: 
https://lists.apache.org/thread/0b8wj8bsocjwhk0t00kcj1pzgjto38n6

I'll proceed with filing the ASF INFRA ticket.

Regards,
James Fredley