Fix flake8 issue

changelog/9.bugfix

@@ -1 +1 @@
-Fix issue of virtualized or containerized environments not reporting the number of CPUs correctly
+Fix issue of virtualized or containerized environments not reporting the number of CPUs correctly.

xdist/plugin.py

@@ -6,13 +6,14 @@ def parse_numprocesses(s):
     if s == 'auto':
         try:
             from os import sched_getaffinity
-            def cpu_count():
-                return len(sched_getaffinity(0))
         except ImportError:
             try:
                 from os import cpu_count
             except ImportError:
                 from multiprocessing import cpu_count
+        else:
+            def cpu_count():
+                return len(sched_getaffinity(0))
 
         try:
             n = cpu_count()