fix: regenerate pb2 files using the latest version of grpcio-tools

[parthea]

Fixes #91 🦕
Fixes #94 🦕

BEGIN_COMMIT_OVERRIDE
fix: regenerate pb2 files using the latest version of grpcio-tools

fix(deps): require protobuf >=1.15.0
END_COMMIT_OVERRIDE

[parthea]

I'll check to make sure the Kokoro test fails before adding the commit to require protobuf >=1.15.0

[parthea]

The unit-3.6 test didn't fail as I expected. It turns out that this test passes locally but other unit-3.x tests fail.
I updated the constraints files for other python versions to see if I can can re-create the test failure in Kokoro

[parthea]

I tested unit-3.6/3.7/3.8/3.9 and only unit-3.9 failed.

nox > Running session unit-3.9
nox > Creating virtual environment (virtualenv) using python3.9 in .nox/unit-3-9
nox > python -m pip install asyncmock pytest-asyncio
nox > python -m pip install mock pytest pytest-cov
nox > python -m pip install -e .
nox > python -m pip install e . -c /tmpfs/src/github/python-api-common-protos/testing/constraints-3.9.txt
nox > py.test --quiet --cov=google/cloud --cov=tests/unit --cov-append --cov-config=.coveragerc --cov-report= --cov-fail-under=0 tests/unit
F                                                                        [100%]
=================================== FAILURES ===================================
______________________________ test_error_reason _______________________________

    def test_error_reason():
>       from google.api import error_reason_pb2

tests/unit/test_google_api_error_reason.py:18:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    """Generated protocol buffer code."""
    from google.protobuf.internal import enum_type_wrapper
    from google.protobuf import descriptor as _descriptor
    from google.protobuf import descriptor_pool as _descriptor_pool
    from google.protobuf import message as _message
    from google.protobuf import reflection as _reflection
    from google.protobuf import symbol_database as _symbol_database

    # @@protoc_insertion_point(imports)

    _sym_db = _symbol_database.Default()


    DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(
        b"\n\x1dgoogle/api/error_reason.proto\x12\ngoogle.api*\xc4\x04\n\x0b\x45rrorReason\x12\x1c\n\x18\x45RROR_REASON_UNSPECIFIED\x10\x00\x12\x14\n\x10SERVICE_DISABLED\x10\x01\x12\x14\n\x10\x42ILLING_DISABLED\x10\x02\x12\x13\n\x0f\x41PI_KEY_INVALID\x10\x03\x12\x1b\n\x17\x41PI_KEY_SERVICE_BLOCKED\x10\x04\x12!\n\x1d\x41PI_KEY_HTTP_REFERRER_BLOCKED\x10\x07\x12\x1e\n\x1a\x41PI_KEY_IP_ADDRESS_BLOCKED\x10\x08\x12\x1f\n\x1b\x41PI_KEY_ANDROID_APP_BLOCKED\x10\t\x12\x1b\n\x17\x41PI_KEY_IOS_APP_BLOCKED\x10\r\x12\x17\n\x13RATE_LIMIT_EXCEEDED\x10\x05\x12\x1b\n\x17RESOURCE_QUOTA_EXCEEDED\x10\x06\x12 \n\x1cLOCATION_TAX_POLICY_VIOLATED\x10\n\x12\x17\n\x13USER_PROJECT_DENIED\x10\x0b\x12\x16\n\x12\x43ONSUMER_SUSPENDED\x10\x0c\x12\x14\n\x10\x43ONSUMER_INVALID\x10\x0e\x12\x1c\n\x18SECURITY_POLICY_VIOLATED\x10\x0f\x12\x18\n\x14\x41\x43\x43\x45SS_TOKEN_EXPIRED\x10\x10\x12#\n\x1f\x41\x43\x43\x45SS_TOKEN_SCOPE_INSUFFICIENT\x10\x11\x12\x19\n\x15\x41\x43\x43OUNT_STATE_INVALID\x10\x12\x12!\n\x1d\x41\x43\x43\x45SS_TOKEN_TYPE_UNSUPPORTED\x10\x13\x42p\n\x0e\x63om.google.apiB\x10\x45rrorReasonProtoP\x01ZCgoogle.golang.org/genproto/googleapis/api/error_reason;error_reason\xa2\x02\x04GAPIb\x06proto3"
    )

>   _ERRORREASON = DESCRIPTOR.enum_types_by_name["ErrorReason"]
E   AttributeError: 'NoneType' object has no attribute 'enum_types_by_name'

google/api/error_reason_pb2.py:36: AttributeError

[busunkim96]

This package has no tests, so it instead runs the unit and system tests of client libraries that take a dependency instead.

This session not meant to be directly run as a session. If you look below at test, it calls unit() and system().

[busunkim96]

With the changes in noxfile.py, I believe the tests are installing googleapis-common-protos from PyPI instead of source.

Note in the log python -m pip install -e . comes after cd python-texttospeech, so . is python-texttospeech, .. is python-api-common-protos.

nox > Session test-3.9(pubsub) was successful.
nox > Running session test-3.9(texttospeech)
nox > Creating virtual environment (virtualenv) using python3.9 in .nox/test-3-9-texttospeech
nox > git -C python-texttospeech pull
Already up to date.
nox > cd python-texttospeech
nox > python -m pip install asyncmock pytest-asyncio
nox > python -m pip install mock pytest pytest-cov
nox > python -m pip install -e . 
nox > python -m pip install e . -c /tmpfs/src/github/python-api-common-protos/testing/constraints-3.9.txt
nox > py.test --quiet --cov=google/cloud --cov=tests/unit --cov-append --cov-config=.coveragerc --cov-report= --cov-fail-under=0 tests/unit