Confirm compatibility with pandas 2.0.0rc0

[khaeru]

This PR:

• Was used to temporarily run the test suite against the pandas 2.0.0rc0 pre-release and confirm all tests pass see here.
• Updates the release notes with details about pandas and Python versions.

Closes #470.

How to review

Read the additions to the release notes and confirm they are clear.

PR checklist

• [x] Continuous integration checks all ✅
• [x] ~Add or expand tests;~ coverage checks both ✅
• ~Add, expand, or update documentation.~ N/A
• [x] Update release notes.

[codecov[bot]]

Codecov Report

Merging #471 (62e1ca8) into main (ac79702) will not change coverage. The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #471   +/-   ##
=====================================
  Coverage   98.5%   98.5%           
=====================================
  Files         42      42           
  Lines       4486    4486           
=====================================
  Hits        4422    4422           
  Misses        64      64           

Impacted Files	Coverage Δ
ixmp/backend/io.py	98.5% <100.0%> (ø)
ixmp/backend/jdbc.py	95.2% <100.0%> (ø)
ixmp/core/scenario.py	97.9% <100.0%> (ø)

[khaeru]

@glatterf42 please merge (merge strategy) once you approve.