fix: update deprecated notificationConfig in healthcare api

[noerog]

Description

Fixes b/310269530

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
  /GoogleCloudPlatform/python-docs-samples/blob/main/.github/CODEOWNERS) with the codeowners for this sample
• Please merge this PR for me once it is approved

[davidcavazos]

File "/workspace/healthcare/api-client/v1/fhir/fhir_stores_test.py", line 244, in test_patch_fhir_store
    fhir_stores.patch_fhir_store(project_id, location, dataset_id, fhir_store_id)
TypeError: patch_fhir_store() missing 1 required positional argument: 'pubsub_topic'

Seems like the test needs to be updated.