tests: schedule_api: slightly increase stack size

Two tests were on the knife-edge of their current stack limit and
were overflowing when UART system calls were added and userspace
enabled.

Test case stack sizes are often pulled out of thin air, the current
value of 256 was just a guess.

Kick these stacks up to 384; verified with sanitycheck --all that
this doesn't break anything.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
2 files changed