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.