perf tests metric-only perf stat: Fix tests 84 and 86 s390

perf tests metric-only perf stat: Fix tests 84 and 86 s390

On s390x KVM and z/VM machines the CPU Measurement Facility is not
available. Events cycles and instructions do not exist.  Running above
tests on s390 KVM and z/VM guests always fail with this error:

  # ./perf test 84 86
  84: perf stat JSON output linter          : FAILED!
  86: perf stat STD output linter           : FAILED!
  #

Root cause is command:

  # perf stat -j --metric-only -e instructions,cycles -- true
  {"metric-value" : "none"}
  #

Which fails due to unsupported events and returns "none".
Do not execute this test case on s390 KVM and z/VM machines.

Output after:
  # ./perf test 84 86
  84: perf stat JSON output linter          : Ok
  86: perf stat STD output linter           : Ok
  #

Fixes: 45a86d017adf4d6c ("perf test: Add --metric-only to perf stat output tests")
Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Suggested-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: https://lore.kernel.org/r/20250424133310.37452-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>