perf tests stat_all_metrics: Fix shellcheck warning SC2076

Fixed shellcheck warning SC2076 in stat_all_metrics.sh.

Before the patch:
shell$ shellcheck stat_all_metrics.sh

In stat_all_metrics.sh line 9:
  if [[ "$result" =~ "${m:0:50}" ]] || [[ "$result" =~ "<not supported>" ]]
                     ^---------^ SC2076: Don't quote right-hand
side of =~, it'll match literally rather than as a regex.

In stat_all_metrics.sh line 15:
  if [[ "$result" =~ "${m:0:50}" ]]
                     ^---------^ SC2076: Don't quote right-hand
side of =~, it'll match literally rather than as a regex.

In stat_all_metrics.sh line 22:
  if [[ "$result" =~ "${m:0:50}" ]]
                     ^---------^ SC2076: Don't quote right-hand
side of =~, it'll match literally rather than as a regex.

After the patch:
shell$ shellcheck stat_all_metrics.sh
shell$
Signed-off-by: Barnali Guha Thakurata <barnali@linux.ibm.com>
Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230613164145.50488-9-atrajeev@linux.vnet.ibm.comSigned-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/stat_all_metrics.sh

@@ -6,20 +6,20 @@ err=0
 for m in $(perf list --raw-dump metrics); do
   echo "Testing $m"
   result=$(perf stat -M "$m" true 2>&1)
-  if [[ "$result" =~ "${m:0:50}" ]] || [[ "$result" =~ "<not supported>" ]]
+  if [[ "$result" =~ ${m:0:50} ]] || [[ "$result" =~ "<not supported>" ]]
   then
     continue
   fi
   # Failed so try system wide.
   result=$(perf stat -M "$m" -a sleep 0.01 2>&1)
-  if [[ "$result" =~ "${m:0:50}" ]]
+  if [[ "$result" =~ ${m:0:50} ]]
   then
     continue
   fi
   # Failed again, possibly the workload was too small so retry with something
   # longer.
   result=$(perf stat -M "$m" perf bench internals synthesize 2>&1)
-  if [[ "$result" =~ "${m:0:50}" ]]
+  if [[ "$result" =~ ${m:0:50} ]]
   then
     continue
   fi