Add support for Python 3.12

[hugovk]

The Python 3.12 beta is now out, let's start testing it: https://dev.to/hugovk/help-test-python-312-beta-1508/

Because pandas doesn't yet support 3.12, we need to skip the pandas-related tests for now. We can do that with pip install --only-binary :all: pandas, which only installs pandas if there's a prebuilt binary wheel available (as it is for 3.7-3.11), and skip when it's not available.

I didn't add the 3.12 Trove classifier yet. We could wait until full release in October, but some other projects have added it already:

• 7 in the top 360: https://pyreadiness.org/3.12/
• 1,083 in total: https://pypi.org/search/?c=Programming+Language+%3A%3A+Python+%3A%3A+3.12

Shall we wait or add it now?

[codecov[bot]]

Codecov Report

Merging #550 (5c02f85) into master (f953e06) will increase coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #550      +/-   ##
==========================================
+ Coverage   91.40%   91.42%   +0.02%     
==========================================
  Files          28       28              
  Lines        2723     2730       +7     
==========================================
+ Hits         2489     2496       +7     
  Misses        234      234              

Impacted Files	Coverage Δ
tests/test_tablib.py	98.74% <100.00%> (+0.01%)	:arrow_up:

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more

[hugovk]

I've added it then, we don't need to remember to do so later :)