Update this repo's orchestrating Pants 2.21 -> 2.23

[huonw]

This just updates the Pants version used for linting etc., should be no functional change.

This requires a few extra changes:

• CI here runs on older versions of macOS that we're removing support for (CI uses pantsbuild's self-hosted macOS runners #421) and thus needs to silence the warnings with allow_deprecated_macos_before_12
  • doing so causes issues with a few tests that ran against this repo's pants.toml with older versions of Pants that don't understand that option, and thus those tests are adjusted to use a dedicated pants.toml
• working around Starting pants shows useless "Initializing Nailgun pool ..." log lines pants#21863