Ensure that the Command Line Interface stops the running Betty application

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.96970% with 3 lines in your changes missing coverage. Please review.

Project coverage is 96.21%. Comparing base (52aaac3) to head (20851a1). Report is 277 commits behind head on 0.4.x.

Files with missing lines	Patch %	Lines
betty/cli/__init__.py	89.28%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 0.4.x #1803 +/- ## ========================================== - Coverage 96.21% 96.21% -0.01% ========================================== Files 259 259 Lines 17922 17925 +3 Branches 3487 3487 ========================================== + Hits 17244 17246 +2 - Misses 456 461 +5 + Partials 222 218 -4 ```

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