### NOTE
* We shouldn't merge this PR until GCP cloud functions drops support for Python 3.7 ([Currently scheduled for GCF](https://cloud.google.com/functions/docs/runtime-support#python))
As part of supporting Python 3.12, we're now officially drop support for Python 3.7.
This PR:
* Changed supported Python version from 3.7 to 3.8 in README.
* Replaced distribution test image from `debian:buster` to `debian:bullseye` since the default Python version in buster is 3.7.
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Closes#34450
PiperOrigin-RevId: 622899511
* Update third_party/protobuf
* run tools/distrib/python/make_grpcio_tools.py
* regenerate protos for ruby, php
* update build_handwritten.yaml
* regenerate projects
* Build - Use :well_known_type_protos instead of :well_known_protos
* Fix target
* Update upb
* Update Python for Protobuf 4.21 (#140)
* Update protobuf dependency on grpcio-tools
* Off by one
* Drop python 3.6 support
* Try upgrading pip
* And in the other script
* Try to figure out if we're compatible with abi3
* See what we've already got installed
* Update the requirements.txt file I didn't know existed
* And here too
* See what's installed
* Let's try that again
* Remove
* Try to confirm version
* Let me see the generated code
* Fix non-Bazel test runner
* Work for all test directories
* Regenerate example protos
* Clean up
* Generate .pyi files
* Fix type checking and linting
* Exclude pyi files from isort
* Upgrade to 3.21.4
* Update iwyu to get around messy protobuf IWYU rules
Co-authored-by: Richard Belleville <gnossen@gmail.com>
* Merge the 3 repeating Python binary compilations
* Restore grpcio_metadata.py
* run_tests.py is running on <3.6
* Restore the Windows gevent version pin
