Fix invalid encoding test w/ Python 3.7 on Linux
Disable mode introduced in Python 3.7:
https://www.python.org/dev/peps/pep-0540/)
@@ -33,6 +33,7 @@ Invalid encoding configuration
... LC_TYPE=invalid
... LANGUAGE=invalid
... LC_ALL=invalid
+ ... PYTHONUTF8=0
... @{COMMAND}
${result} = Run Process
... echo "redirect stdin" | ${cmd}
