Include tests in source tarball

[matbryan52]

Include tests in source tarball to allow testing during conda-build

Contributor Checklist:

• I have added or updated my entry in the creators.json file
• I have added a changelog entry for my contribution
• I have added/updated documentation for all user-facing changes
• I have added/updated test cases

Reviewer Checklist:

• /azp run libertem.libertem-live-data passed

[sk1p]

/azp run libertem.libertem-live-data

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.06 ⚠️

Comparison is base (07352b9) 79.39% compared to head (0989153) 79.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
- Coverage   79.39%   79.33%   -0.06%     
==========================================
  Files          35       35              
  Lines        3382     3382              
  Branches      451      451              
==========================================
- Hits         2685     2683       -2     
- Misses        563      564       +1     
- Partials      134      135       +1     

see 1 file with indirect coverage changes

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[sk1p]

FYI I pushed into this PR, as the current MANIFEST.in was a bit liberal when choosing what files to include - for example, the v0.2.0 wheel/sdist includes some __pycache__ files, and if I build it from my laptop, it also includes the (quite large) .mypy_cache directory. Tests should still be properly contained in the sdist. Also included two drive-by fixes for correctness.

[sk1p]

/azp run libertem.libertem-live-data

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).