tests: posix: fs: increase ztest stack size from 1k to 2k

The default stack size was causing qemu_arc/qemu_arc_em and
qemu_arc/qemu_arc_hs to fail when a dirent object was
stack-allocated.

Increase the default stack size to accomodate for additional
usage.

Signed-off-by: Chris Friedt <[email protected]>

Author: cfriedt

tests/posix/fs/prj.conf

@@ -5,4 +5,5 @@ CONFIG_POSIX_API=y
 CONFIG_POSIX_FILE_SYSTEM=y
 CONFIG_ZTEST=y
 CONFIG_MAIN_STACK_SIZE=4096
+CONFIG_ZTEST_STACK_SIZE=2048
 CONFIG_EVENTFD=n