fix: writing views of backed anndata objects

[ilan-gold]

I'm kind of punting on knowing that the intention of changing the backing file is after writing. I'm genuinely not sure what this feature would be for other than what I am testing i.e., why would you rewrite a non-view of a backed file in its entirety?

• Closes Problems saving backed anndata in chunks #2077
• Tests added
• Release note added (or unnecessary)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.57%. Comparing base (e6fbb70) to head (27f2927).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2092   +/-   ##
=======================================
  Coverage   85.57%   85.57%           
=======================================
  Files          46       46           
  Lines        7070     7070           
=======================================
  Hits         6050     6050           
  Misses       1020     1020           

Files with missing lines	Coverage Δ
src/anndata/_core/anndata.py	83.07% <100.00%> (ø)

[flying-sheep]

this makes sense, only the release note text confuses me!