Add default for num_cpu in case it returns None to avoid division error

Author: xrmx

instrumentation/opentelemetry-instrumentation-system-metrics/src/opentelemetry/instrumentation/system_metrics/__init__.py

@@ -798,7 +798,8 @@ def _get_cpu_utilization(
     ) -> Iterable[Observation]:
         """Observer callback for CPU utilization"""
         proc_cpu_percent = self._proc.cpu_percent()
-        num_cpus = psutil.cpu_count()
+        # may return None so add a default of 1 in case
+        num_cpus = psutil.cpu_count() or 1
         yield Observation(
             proc_cpu_percent / 100 / num_cpus,
             self._cpu_utilization_labels.copy(),