MEDIUM: tasks: Use __ha_barrier_store after modifying global_tasks_mask.

MEDIUM: tasks: Use __ha_barrier_store after modifying global_tasks_mask.

Now that we no longer use atomic operations to update global_tasks_mask,
as it's always modified while holding the TASK_RQ_LOCK, we have to use
__ha_barrier_store() instead of __ha_barrier_atomic_store() to ensure
any modification of global_tasks_mask is seen before modifying
active_tasks_mask.

This should be backported to 1.9.