Fix detection of ModemManager (#7076)

lib/python/qmk/cli/doctor.py

@@ -52,10 +52,10 @@ def doctor(cli):
         if shutil.which('systemctl'):
             mm_check = subprocess.run(['systemctl', 'list-unit-files'], stdout=subprocess.PIPE, stderr=subprocess.PIPE, timeout=10, universal_newlines=True)
             if mm_check.returncode == 0:
-                mm = True
+                mm = False
                 for line in mm_check.stdout.split('\n'):
                     if 'ModemManager' in line and 'enabled' in line:
-                        mm = False
+                        mm = True
 
                 if mm:
                     cli.log.warn("{bg_yellow}Detected ModemManager. Please disable it if you are using a Pro-Micro.")