fix(cloudrunv2): Resolve persistent diff on WorkerPool scaling_mode

The `google_cloud_run_v2_worker_pool` resource showed a perpetual diff
on the `scaling.scaling_mode` field. When the `scaling` block was
configured (e.g., with `manual_instance_count`) but `scaling_mode` was
omitted, Terraform would try to remove the `scaling_mode` attribute
on subsequent plans.

This occurred because the Cloud Run API defaults `scaling_mode` to "MANUAL"
if not specified, but the Terraform resource schema did not account for
this server-side default.

This commit adds `default_from_api: true` to the `scaling.scaling_mode`
field in the magic-modules YAML definition. This informs the provider
that the API may return a default value for this field, preventing
Terraform from detecting a diff when the API provides the "MANUAL" value
that isn't explicitly in the configuration.

Author: kminsu-google

mmv1/products/cloudrunv2/WorkerPool.yaml

@@ -294,6 +294,7 @@ properties:
         type: Enum
         description: |
           The scaling mode for the worker pool. It defaults to MANUAL.
+        default_from_api: true
         enum_values:
           - 'AUTOMATIC'
           - 'MANUAL'