Fix TimeSince primitive. Make it work with all Datetime subclasses

[monti-python]

Pull Request Description

fixes #1047

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #1048 into main will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1048      +/-   ##
==========================================
+ Coverage   98.33%   98.35%   +0.01%     
==========================================
  Files         126      126              
  Lines       13033    13039       +6     
==========================================
+ Hits        12816    12824       +8     
+ Misses        217      215       -2     

Impacted Files	Coverage Δ
...retools/primitives/standard/transform_primitive.py	100.00% <100.00%> (ø)
...s/tests/primitive_tests/test_transform_features.py	98.81% <100.00%> (+0.01%)	⬆️
featuretools/synthesis/deep_feature_synthesis.py	97.83% <0.00%> (+0.48%)	⬆️

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[thehomebrewnerd]

Please merge in the latest changes from the Featuretools main branch. After doing this, verify your new changelog entry is in the proper location. Also, please add your username to the list of contributors in the Future Release section.

[monti-python]

@thehomebrewnerd I've updated the PR, thanks for reviewing!

[thehomebrewnerd]

@monti-python Thanks for the contribution!

[rwedge]

PR looks good, thanks for the contribution!

I updated the wording of the changelog entry a bit