chore: upgrade (flask-)sqlalchemy

[goerch]

I'm currently interested in getting the tests to run. It would be great to get some guidance if and how we should handle and test compatibility of the PR w.r.t. older versions of SQLAlchemy?

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (59db85d) 79.31% compared to head (67729a0) 79.28%.

Files	Patch %	Lines
flask_appbuilder/models/sqla/__init__.py	57.14%	6 Missing ⚠️
flask_appbuilder/cli.py	0.00%	1 Missing ⚠️
flask_appbuilder/models/sqla/interface.py	85.71%	1 Missing ⚠️
flask_appbuilder/security/sqla/manager.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2162      +/-   ##
==========================================
- Coverage   79.31%   79.28%   -0.04%     
==========================================
  Files          72       72              
  Lines        8974     8953      -21     
==========================================
- Hits         7118     7098      -20     
+ Misses       1856     1855       -1     

Flag	Coverage Δ
python	79.28% <76.92%> (-0.04%)	⬇️

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[zacqed]

@dpgaspar would you be able to review this. many thanks