Forgot the f in f-strings, corrected.

mnpw/nagios.py

@@ -165,9 +165,9 @@ class Check:
         self.ExitCode = proc.returncode
         logging.info(f"Exit code is {self.ExitCode}.")
         self._stdout = proc.stdout
-        logging.info("stdout is {self._stdout}.")
+        logging.info(f"stdout is {self._stdout}.")
         self.stderr = proc.stderr
-        logging.info("stderr is {self.stderr}.")
+        logging.info(f"stderr is {self.stderr}.")
         if self.ExitCode in list(NagiosCode):
             self._parse_output()
             logging.info(f"Output is {self.Output}.")