CI: match and trim out internal timestamp for test prefix

Adjust the regexes to match the test line with timestamps, then remove
them for the summary. The internal timestamp is still in the full logs.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17045