feat: change the tag to prevent assignbot assigning a reviewer to 'no-assignbot'

BREAKING CHANGE: assignbot will ignore the 'no-assignbot' tag, and not the 'client-project'

previously the tag was 'client-project', but it was not very well chosen as some
client project may need assignbot's help, and some non-client-project may no
need it.

Let's use a proper tag for this.
2 jobs for topic/default/change-ignored-tag in 26 seconds (queued for 17 seconds)
Status Job ID Name Coverage
  Lint
passed lint_black #93873

00:00:26

passed lint_flake8 #93874

00:00:18