Tests: Add example for StringListParamType interference when running cli multiple times

[gutzbenj]

Dear all, dear @lewoudar ,

this PR is meant to show some issue that we ran into within our test suite for wetterdienst at [1]. It accompanies the issue #22 . The second assert would currently fail.

Sincerely, Benjamin

/CC @amotl

[1] https://github.com/earthobservations/wetterdienst

[codecov-commenter]

Codecov Report

Base: 100% // Head: 100% // No change to project coverage :thumbsup:

Coverage data is based on head (d2d14a8) compared to base (daf87d9). Patch coverage: 100% of modified lines in pull request are covered.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #23 +/- ## ===================================== Coverage 100% 100% ===================================== Files 8 8 Lines 341 339 -2 ===================================== - Hits 341 339 -2 ``` | [Impacted Files](https://codecov.io/gh/click-contrib/click_params/pull/23?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [click\_params/base.py](https://codecov.io/gh/click-contrib/click_params/pull/23?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y2xpY2tfcGFyYW1zL2Jhc2UucHk=) | `100% <100%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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[lewoudar]

Ok, seems like Windows CI is not working, I'm sure of the issue, can you try to update dependencies to see if it works better?

[lewoudar]

Also, I just saw it now, can you remove the private attribute self._convert_called and the places where it is used in tests, please

[gutzbenj]

Done!

[lewoudar]

Thanks for the work @gutzbenj I will probably update some dependencies before releasing a new version this week :)