Allow to pass arguments to pytest via runner-options argument

[yakky]

Description

Pass arguments to pytest when using pytest runner via existing runner-options argument is more flexible than using var environments

References

Fix #159

Checklist

• I have read the contribution guide
• Code lint checked via inv lint
• changes file included (see docs)
• Usage documentation added in case of new features
• Tests added

[codecov]

Codecov Report

Merging #163 into develop will increase coverage by 0.34%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #163      +/-   ##
===========================================
+ Coverage    91.34%   91.69%   +0.34%     
===========================================
  Files            6        6              
  Lines          693      698       +5     
  Branches       114      115       +1     
===========================================
+ Hits           633      640       +7     
+ Misses          21       20       -1     
+ Partials        39       38       -1     

Flag	Coverage Δ
#unittests	91.69% <100.00%> (+0.34%)	⬆️

Impacted Files	Coverage Δ
app_helper/main.py	88.37% <100.00%> (+1.31%)	⬆️
app_helper/pytest_runner.py	100.00% <100.00%> (ø)

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