ZTS: zed_synchronous_zedlet failures

[tonyhutter]

System information

Type	Version/Name
Distribution Name	Debian and others
Distribution Version
Kernel Version
Architecture
OpenZFS Version

Describe the problem you're observing

We've seen an uptick in zed_synchronous_zedlet ZTS failures. Example:
https://github.com/openzfs/zfs/actions/runs/21771045624/job/62999810149?pr=18161

Describe how to reproduce the problem

Run ZTS in CI

Include any warning/errors/backtraces from the system logs

Looks like it times out waiting for a trim_finish event after a pool trim.

[2026-02-07T02:32:42.074094] Test (Linux): /usr/share/zfs/zfs-tests/tests/functional/events/zed_synchronous_zedlet (run as root) [00:11] [FAIL]
02:32:30.25 ASSERTION: Verify ZED synchronous zedlets work as expected           
02:32:30.25 SUCCESS: truncate -s 100M /var/tmp/vdev-file-sync-zedlet             
02:32:30.31 SUCCESS: zpool create testpool2 /var/tmp/vdev-file-sync-zedlet       
02:32:30.34 SUCCESS: zpool scrub -w testpool2                                    
02:32:30.40 cleared 6522 events                                                  
02:32:30.40 SUCCESS: zpool events -c                                             
02:32:30.41 SUCCESS: chmod +x /var/tmp/zed/scrub_start-async.sh                  
02:32:30.41 SUCCESS: chmod +x /var/tmp/zed/scrub_start-slow.sh                   
02:32:30.42 SUCCESS: chmod +x /var/tmp/zed/scrub_finish-sync-slow.sh             
02:32:30.42 SUCCESS: chmod +x /var/tmp/zed/trim_start-async.sh                   
02:32:30.44 NOTE: Starting ZED                                                   
02:32:30.44 SUCCESS: truncate -s 0 /var/tmp/zed/zed.debug.log                    
02:32:30.44 SUCCESS: eval zed -vF -d /var/tmp/zed -P /var/tmp/constrained_path.IwSDc2 -s /var/tmp/zed/state -j 1 2>/var/tmp/zed/zed.log &
02:32:30.45 SUCCESS: zed_start                                                   
02:32:30.48 SUCCESS: zpool scrub -w testpool2                                    
02:32:30.52 SUCCESS: zpool trim -w testpool2                                     
02:32:40.57 file_wait_event exceeded 10.041 seconds                              
02:32:40.57 ERROR: file_wait_event /var/tmp/zed/zed.debug.log sysevent\.fs\.zfs\.trim_finish 10 exited 1

[tonyhutter]

I'm testing a fix