ZTS: Retry auto_spare_multiple.ksh

The auto_spare_multiple.ksh test may incorrectly fail for a similar
reason as the auto_spare_shared.ksh test. Add it to known list of
exceptions which should be retried to prevent failures in the CI.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13318