tests: spinlock: Increase thread execution to prevent quick exit

On Intel boards (like intel_ehl_crb and intel_rpl_s_crb) for the
trylock_test some part is executed very fast and since there is no
synchronization, there might be situation when there is no
trylock_failures. Increasing time spend in this part fixes the issue.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>