build: bump version, draft change log.

[janfb]

• add 23.1 content to changelog
• draft content for 23.2

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.34%. Comparing base (dbcd06b) to head (d985424).
Report is 5 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1274       +/-   ##
===========================================
- Coverage   89.25%   78.34%   -10.91%     
===========================================
  Files         119      119               
  Lines        8698     8705        +7     
===========================================
- Hits         7763     6820      -943     
- Misses        935     1885      +950     

Flag	Coverage Δ
unittests	78.34% <100.00%> (-10.91%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sbi/__version__.py	100.00% <100.00%> (ø)

... and 37 files with indirect coverage changes

[michaeldeistler]

LGTM!