bitbake: runqueue: Small but critical fix

bitbake: runqueue: Small but critical fix

We've observed do_package and do_package_setscene running in parallel. The
reason is that holdoff_tasks wasn't getting updated. Looking at the code, it
would seem the reason is that the task was in pending_migrations and hence
changed wasn't set and holdoff_tasks wasn't updated.

Fix this. It only affects builds with rehashing enabled.

(Bitbake rev: e26e61e84575669bd223f6ab316798097ed95ec8)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>