chore!: Drop support for Python 3.7, put minimum version limit on Black

[dbanty]

No description provided.

[codecov]

Codecov Report

Merging #754 (bfbb919) into main (88e79ba) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #754   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           49        49           
  Lines         1978      1971    -7     
=========================================
- Hits          1978      1971    -7     

Impacted Files	Coverage Δ
openapi_python_client/cli.py	100.00% <ø> (ø)
openapi_python_client/parser/openapi.py	100.00% <ø> (ø)
openapi_python_client/__init__.py	100.00% <100.00%> (ø)
..._client/schema/openapi_schema_pydantic/open_api.py	100.00% <100.00%> (ø)

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