creating an enum class used to be quadratic in the number of fields, in
two different places: in the dicitonary implementation for the enum
class, and when setting the name of all members. fix the former by
switching to a dictionary instead of a list to store the fields
while building up the dictionary. fix the latter by trying to use the
already existing dictionary when looking up a field, instead of looping
of all fields.

There are two changes:

Changes in the actual code:

 - _member_names changed from a list to a dict in python/cpython#28907
    - we instance-check and remove by list-specific or dict-specific way

Change in the tests only:

 - accessing other enum members via instance attributes is no longer possible
    - we access them via the class instead
    - we leave the original test in a try-except block

Some of the Python enum changes might get reverted,
see python/cpython#93910
But the fix is backwards compatible.

There are two changes:

Changes in the actual code:

 - _member_names changed from a list to a dict in python/cpython#28907
    - we instance-check and remove by list-specific or dict-specific way

Change in the tests only:

 - accessing other enum members via instance attributes is no longer possible
    - we access them via the class instead
    - we leave the original test in a try-except block

Some of the Python enum changes might get reverted,
see python/cpython#93910
But the fix is backwards compatible.

Fixes googleapis#326

* Adjust to enum changes in Python 3.11.0b3

There are two changes:

Changes in the actual code:

 - _member_names changed from a list to a dict in python/cpython#28907
    - we instance-check and remove by list-specific or dict-specific way

Change in the tests only:

 - accessing other enum members via instance attributes is no longer possible
    - we access them via the class instead
    - we leave the original test in a try-except block

Some of the Python enum changes might get reverted,
see python/cpython#93910
But the fix is backwards compatible.

Fixes #326

* ci: unit test session with python 3.11.0-beta.3

* ci: add python v3.11.0-beta.3 to noxfile.py

* another attempt to get python 3.11.0b3 working in github actions

* ci: use python 3.8 for docs check

* ci: fix docs build

* fix ci

* mark python 3.11 tests as required

* add python 3.11 to setup.py

* fix docs build

* remove python 3.11 test for unitcpp

* remove python 3.11 test for unitcpp

* remove python 3.11 test for unitcpp

* attempt to fix exclude in github action

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

* Adjust to enum changes in Python 3.11.0b3

There are two changes:

Changes in the actual code:

 - _member_names changed from a list to a dict in python/cpython#28907
    - we instance-check and remove by list-specific or dict-specific way

Change in the tests only:

 - accessing other enum members via instance attributes is no longer possible
    - we access them via the class instead
    - we leave the original test in a try-except block

Some of the Python enum changes might get reverted,
see python/cpython#93910
But the fix is backwards compatible.

Fixes googleapis/proto-plus-python#326

* ci: unit test session with python 3.11.0-beta.3

* ci: add python v3.11.0-beta.3 to noxfile.py

* another attempt to get python 3.11.0b3 working in github actions

* ci: use python 3.8 for docs check

* ci: fix docs build

* fix ci

* mark python 3.11 tests as required

* add python 3.11 to setup.py

* fix docs build

* remove python 3.11 test for unitcpp

* remove python 3.11 test for unitcpp

* remove python 3.11 test for unitcpp

* attempt to fix exclude in github action

Co-authored-by: Anthonios Partheniou <partheniou@google.com>