…ge (#14999)

Fixes test failures such as
https://btx.cloud.google.com/invocations/046f57c8-7637-4cc8-9cf3-02a45fb1b063

It seems to have been caused by the recent changes in auth:
googleapis/google-auth-library-python#1919
googleapis/google-auth-library-python#1590


Example error log:
```
_ ERROR collecting tests/unit/gapic/bigquery_storage_v1/test_big_query_read.py _
ImportError while importing test module '/tmpfs/src/github/google-cloud-python/packages/google-cloud-bigquery-storage/tests/unit/gapic/bigquery_storage_v1/test_big_query_read.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/local/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/unit/gapic/bigquery_storage_v1/test_big_query_read.py:42: in 
    from google.api_core import gapic_v1, grpc_helpers, grpc_helpers_async, path_template
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/api_core/gapic_v1/__init__.py:18: in 
    from google.api_core.gapic_v1 import method
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/api_core/gapic_v1/method.py:24: in 
    from google.api_core import grpc_helpers
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/api_core/grpc_helpers.py:23: in 
    import google.auth.transport.grpc
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/auth/transport/grpc.py:23: in 
    from google.oauth2 import service_account
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/oauth2/service_account.py:78: in 
    from google.auth import _service_account_info
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/auth/_service_account_info.py:20: in 
    from google.auth import crypt
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/auth/crypt/__init__.py:41: in 
    from google.auth.crypt import es
.nox/prerelease_deps-protobuf_implementation-python/lib/python3.14/site-packages/google/auth/crypt/es.py:21: in 
    import cryptography.exceptions
E   ModuleNotFoundError: No module named 'cryptography'
```