mypy typing errors for batch enum's

### Determine this is the right repository

- [X] I determined this is the correct repository in which to report this bug.

### Summary of the issue

**Context**
Running `mypy` on [this official code sample ](https://cloud.google.com/batch/docs/samples/batch-create-container-job#batch_create_container_job-python) (copy and paste into a file `batch_example.py` and running `mypy batch_example.py`)

**Expected Behavior:**
No mypy errors

**Actual Behavior:**
mypy errors:

```shell
batch_example.py:66: error: Incompatible types in assignment (expression has type "int", variable has type "Destination") [assignment]
Found 1 error in 1 file (checked 1 source file)
```

### API client name and version

google-cloud-batch v0.17.28

### Reproduction steps: code

```python
from google.cloud import batch_v1

def create_container_job(project_id: str, region: str, job_name: str) -> batch_v1.Job:
"""
This method shows how to create a sample Batch Job that will run
a simple command inside a container on Cloud Compute instances.

Args:
project_id: project ID or project number of the Cloud project you want to use.
region: name of the region you want to use to run the job. Regions that are
available for Batch are listed on: https://cloud.google.com/batch/docs/get-started#locations
job_name: the name of the job that will be created.
It needs to be unique for each project and region pair.

Returns:
A job object representing the job created.
"""
client = batch_v1.BatchServiceClient()

# Define what will be done as part of the job.
runnable = batch_v1.Runnable()
runnable.container = batch_v1.Runnable.Container()
runnable.container.image_uri = "gcr.io/google-containers/busybox"
runnable.container.entrypoint = "/bin/sh"
runnable.container.commands = [
"-c",
"echo Hello world! This is task ${BATCH_TASK_INDEX}. This job has a total of ${BATCH_TASK_COUNT} tasks.",
]

# Jobs can be divided into tasks. In this case, we have only one task.
task = batch_v1.TaskSpec()
task.runnables = [runnable]

# We can specify what resources are requested by each task.
resources = batch_v1.ComputeResource()
resources.cpu_milli = 2000 # in milliseconds per cpu-second. This means the task requires 2 whole CPUs.
resources.memory_mib = 16 # in MiB
task.compute_resource = resources

task.max_retry_count = 2
task.max_run_duration = "3600s"

# Tasks are grouped inside a job using TaskGroups.
# Currently, it's possible to have only one task group.
group = batch_v1.TaskGroup()
group.task_count = 4
group.task_spec = task

# Policies are used to define on what kind of virtual machines the tasks will run on.
# In this case, we tell the system to use "e2-standard-4" machine type.
# Read more about machine types here: https://cloud.google.com/compute/docs/machine-types
policy = batch_v1.AllocationPolicy.InstancePolicy()
policy.machine_type = "e2-standard-4"
instances = batch_v1.AllocationPolicy.InstancePolicyOrTemplate()
instances.policy = policy
allocation_policy = batch_v1.AllocationPolicy()
allocation_policy.instances = [instances]

job = batch_v1.Job()
job.task_groups = [group]
job.allocation_policy = allocation_policy
job.labels = {"env": "testing", "type": "container"}
# We use Cloud Logging as it's an out of the box available option
job.logs_policy = batch_v1.LogsPolicy()
job.logs_policy.destination = batch_v1.LogsPolicy.Destination.CLOUD_LOGGING

create_request = batch_v1.CreateJobRequest()
create_request.job = job
create_request.job_id = job_name
# The job's parent is the region in which the job will run
create_request.parent = f"projects/{project_id}/locations/{region}"

return client.create_job(create_request)
```

### Reproduction steps: supporting files

_No response_

### Reproduction steps: actual results

```shell
batch_example.py:66: error: Incompatible types in assignment (expression has type "int", variable has type "Destination") [assignment]
Found 1 error in 1 file (checked 1 source file)
```

### Reproduction steps: expected results

```shell
Success: no issues found in 1 source file
```

### OS & version + platform

macOS 15.0.1

### Python environment

Python 3.11.10

### Python dependencies

```
Package Version
------------------------ ---------
cachetools 5.5.0
certifi 2024.8.30
charset-normalizer 3.3.2
google-api-core 2.20.0
google-auth 2.35.0
google-cloud-batch 0.17.28
googleapis-common-protos 1.65.0
grpcio 1.66.2
grpcio-status 1.66.2
idna 3.10
mypy 1.11.2
mypy-extensions 1.0.0
pip 24.2
proto-plus 1.24.0
protobuf 5.28.2
pyasn1 0.6.1
pyasn1_modules 0.4.1
requests 2.32.3
rsa 4.9
setuptools 75.1.0
typing_extensions 4.12.2
urllib3 2.2.3
```