tests/unit: test_metrics_emission_with_failure_attempt fails due to lack of "intercept"

[odeke-em]

This is the failure output

_________________________________________________ test_metrics_emission_with_failure_attempt _________________________________________________

patched_client = <google.cloud.spanner_v1.client.Client object at 0x10d7faaf0>

    def test_metrics_emission_with_failure_attempt(patched_client):
        instance = patched_client.instance("test-instance")
        database = instance.database("example-db")
        factory = SpannerMetricsTracerFactory()
    
        assert factory.enabled
    
        transport = database.spanner_api._transport
        metrics_interceptor = transport._metrics_interceptor
>       original_intercept = metrics_interceptor.intercept
E       AttributeError: 'NoneType' object has no attribute 'intercept'

tests/unit/test_metrics.py:58: AttributeError
------------------------------------------------------------- Captured log setup -------------------------------------------------------------
WARNING  opentelemetry.metrics._internal:__init__.py:864 Overriding of current MeterProvider is not allowed
----------------------------------------------------------- Captured log teardown ------------------------------------------------------------
WARNING  opentelemetry.metrics._internal:__init__.py:864 Overriding of current MeterProvider is not allowed
============================================================== warnings summary ==============================================================