IndexError in _tqdm_helpers.wait_for_query when query_plan changes between iterations

## Environment details

- OS: Linux (GKE container)
- Python: 3.12
- `google-cloud-bigquery` version: 3.30.0 (also confirmed present on latest `main`)

## Steps to reproduce

Call `query_job.to_geodataframe(progress_bar_type="tqdm", ...)` on a query that takes longer than 0.5s. The issue is intermittent and affects a small fraction of queries. In my particular example it was a MERGE query, could be that it's some edge case related to how those plans are expressed? But I ran a batch of a dozen of these queries and only 2 hit the issue (and I've also never seen it before despite running this same structure of query many times).

## Stack trace

```
File "google/cloud/bigquery/job/query.py", line 2154, in to_geodataframe
query_result = wait_for_query(self, progress_bar_type, max_results=max_results)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "google/cloud/bigquery/_tqdm_helpers.py", line 113, in wait_for_query
current_stage = query_job.query_plan[i]
~~~~~~~~~~~~~~~~~~~~^^^
IndexError: list index out of range
```

## Description

In [`_tqdm_helpers.py:wait_for_query`](https://github.com/googleapis/google-cloud-python/blob/main/packages/google-cloud-bigquery/google/cloud/bigquery/_tqdm_helpers.py#L109-L134), the index `i` is incremented on line 133 whenever a completed stage is detected, but the bounds check on line 131 (`i < default_total - 1`) uses `default_total` from the current iteration. On the next iteration, `query_job.query_plan` is re-read (line 111-113) after `reload()` has refreshed the job state from the server, and its length may no longer be consistent with `i`.

```python
i = 0
while True:
if query_job.query_plan:
default_total = len(query_job.query_plan)
current_stage = query_job.query_plan[i] # <-- IndexError here
...
try:
query_result = query_job.result(timeout=0.5)
...
break
except concurrent.futures.TimeoutError:
query_job.reload()
if current_stage:
if current_stage.status == "COMPLETE":
if i < default_total - 1:
progress_bar.update(i + 1)
i += 1
continue
```

There is no bounds check on `i` before accessing `query_job.query_plan[i]` on line 113. Adding something like `if i < len(query_job.query_plan)` before the access would prevent the IndexError.