tests: revert back to original coredump patterns on Linux, too

tests: revert back to original coredump patterns on Linux, too

Otherwise, they leak past the tests and contaminate the running system,
breaking coredumps entirely

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Co-authored-by: Yannick Le Pennec <yannick.lepennec@live.fr>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13259