Missing import in `**/types/__init__.py` for certain enums

[parthea]

See the link to the generated code below for google/cloud/aiplatform/v1beta1 where the import statement for AcceleratorType is missing in google/cloud/aiplatform_v1beta1/types/__init__.py.

https://github.com/googleapis/googleapis-gen/blob/6b2c01cabe29e8c7de08852efaef631ff18d62b4/google/cloud/aiplatform/v1beta1/aiplatform-v1beta1-py/google/cloud/aiplatform_v1beta1/types/__init__.py#L850C6-L850C21

See the definition for AcceleratorType in the proto here:
https://github.com/googleapis/googleapis/blob/2fd7625cf9808234503fd5addc6e2bda8fe5c114/google/cloud/aiplatform/v1beta1/accelerator_type.proto#L28

The init file should have

from .accelerator_type import (
    AcceleratorType,
)

The issue is that enums which are not part of messages are not added to __init__.py because of the proto.messages conditional check

gapic-generator-python/gapic/templates/%namespace/%name_%version/%sub/types/__init__.py.j2

Lines 5 to 14 in 90ba3f7

	{% for _, proto in api.protos|dictsort if proto.file_to_generate and proto.messages %}
	from .{{proto.module_name }} import (
	{% for _, message in proto.messages|dictsort %}
	{{message.name }},
	{% endfor %}
	{% for _, enum in proto.enums|dictsort %}
	{{ enum.name }},
	{% endfor %}
	)
	{% endfor %}