BUG: fix index error pfs_mean_speed

[bifbof]

Fixes #449

Apparently the behavior of pd.merge changed after an update.
Other places in the code should not be affected by the pd.merge change.

Also fix error in test where override of geometry column resulted in cast to Series with object type.

[codecov]

Codecov Report

Base: 98.06% // Head: 97.98% // Decreases project coverage by -0.08% ⚠️

Coverage data is based on head (47ff2b7) compared to base (56176cb).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #450      +/-   ##
==========================================
- Coverage   98.06%   97.98%   -0.09%     
==========================================
  Files          39       32       -7     
  Lines        1858     1783      -75     
  Branches      261      261              
==========================================
- Hits         1822     1747      -75     
  Misses         14       14              
  Partials       22       22              

Impacted Files	Coverage Δ
trackintel/model/util.py	100.00% <100.00%> (ø)
trackintel/analysis/__init__.py
trackintel/visualization/__init__.py
trackintel/model/__init__.py
trackintel/geogr/__init__.py
trackintel/__init__.py
trackintel/io/__init__.py
trackintel/preprocessing/__init__.py

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[NinaWie]

Thanks for fixing the tests! I left one comment. If you think that case cannot occur, feel free to merge.
I don't get why one of the coverage checks fails. The coverage should be the same, so I think we can ignore it.

[bifbof]

Ready for merge. :)
As for the coverage apparently they don't include the __init__ files anymore → therefor we got a unrelated decrease there.