Invalid escape sequence fixes

[scop]

No description provided.

[codecov]

Codecov Report

Merging #638 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #638   +/-   ##
=======================================
  Coverage   93.95%   93.95%           
=======================================
  Files          11       11           
  Lines        2364     2364           
=======================================
  Hits         2221     2221           
  Misses        143      143

Impacted Files	Coverage Δ
tox/interpreters.py	82.03% <ø> (ø)	⬆️
tox/config.py	97.57% <100%> (ø)	⬆️
tox/session.py	94.34% <100%> (ø)	⬆️

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[The-Compiler]

I'm wondering why we didn't notice earlier? Maybe it'd be a good idea to turn on -Werror for the testsuite?

[obestwalter]

woah - if I run pytest -Werror basically everything fails for using old pytest constructs ...