chore: use gapic-generator-python 0.58.4 (#8)

* chore: use gapic-generator-python 0.58.4

fix: provide appropriate mock values for message body fields

committer: dovs
PiperOrigin-RevId: 419025932

Source-Link: googleapis/googleapis@73da669

Source-Link: https://github.com/googleapis/googleapis-gen/commit/46df624a54b9ed47c1a7eefb7a49413cf7b82f98
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google/cloud/vmmigration_v1/services/vm_migration/transports/base.py

@@ -103,7 +103,6 @@ def __init__(
             credentials, _ = google.auth.load_credentials_from_file(
                 credentials_file, **scopes_kwargs, quota_project_id=quota_project_id
             )
-
         elif credentials is None:
             credentials, _ = google.auth.default(
                 **scopes_kwargs, quota_project_id=quota_project_id