tests: kernel: sched: schedule_api: Increase stack size.
tests: kernel: sched: schedule_api: Increase stack size.

The stack size was way too less. Increasing the size to minimum
of 512 for all platforms.

Signed-off-by: Adithya Baglody <06b44f6fa9a97a2b955c2d2cd070279967447860@intel.com>

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