selftests/filesystems: grant executable permission to run_fat_tests.sh

When use tools/testing/selftests/kselftest_install.sh to make the
kselftest-list.txt under tools/testing/selftests/kselftest_install.

Then use tools/testing/selftests/kselftest_install/run_kselftest.sh to run
all the kselftests in kselftest-list.txt, it will be blocked by case
"filesystems/fat: run_fat_tests.sh" with "Warning: file run_fat_tests.sh
is not executable", so grant executable permission to run_fat_tests.sh to
fix this issue.

Link: https://lkml.kernel.org/r/dfdbba6df8a1ab34bb1e81cd8bd7ca3f9ed5c369.1673424747.git.pengfei.xu@intel.com
Fixes: dd7c9be ("selftests/filesystems: add a vfat RENAME_EXCHANGE test")
Signed-off-by: Pengfei Xu <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Pengfei Xu