Make fctx->attributes atomic.
requested to merge 1412-threadsanitizer-data-race-resolver-c-7030-in-fctx_decreference-2-v9_14 into v9_14
FCTX_ATTR_SHUTTINGDOWN needs to be set and tested while holding the node lock but the rest of the attributes don't as they are task locked. Making fctx->attributes atomic allows both behaviours without races.
(cherry picked from commit 912ce874)
Closes #1412 (closed)