perf tests: Ignore shellcheck warning in lock_contention

perf tests: Ignore shellcheck warning in lock_contention

Running shellcheck on lock_contention.sh generates below
warning

	In tests/shell/lock_contention.sh line 36:
	   if [ `nproc` -lt 4 ]; then
		  ^-----^ SC2046: Quote this to prevent word splitting.

Here since nproc will generate a single word output
and there is no possibility of word splitting, this
warning can be ignored. Use exception for this with
"disable" option in shellcheck. This warning is observed
after commit:
"commit 29441ab3a30a ("perf test lock_contention.sh: Skip test
if not enough CPUs")"

Fixes: 29441ab3a30a ("perf test lock_contention.sh: Skip test if not enough CPUs")
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: maddy@linux.ibm.com
Cc: disgoel@linux.vnet.ibm.com
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20231013073021.99794-2-atrajeev@linux.vnet.ibm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>