[import-profiler]: remove import-profiler skip workaround once Python 3.15 is officially released

## Context
A temporary skip was added to `ci/run_single_test.sh` ([]) for packages with heavy native/scientific dependencies (`bigframes`, `pandas-gbq`, `google-cloud-documentai-toolbox`, `db-dtypes`, `bigquery-magics`) that lack pre-built binary wheels on PyPI during Python 3.15 pre-releases.

## Action Items
Once Python 3.15 is officially released and upstream binary wheels (`numpy`, `pandas`, `pyarrow`, etc.) are on PyPI:

- [ ] Remove `UNSUPPORTED_PRE_RELEASE_PACKAGES` from `ci/run_single_test.sh`.
- [ ] Verify `import-profiler` runs successfully across all packages.

## Related PR
* Workaround PR: https://github.com/googleapis/google-cloud-python/pull/18033
* Workflow: [`.github/workflows/import-profiler.yml`](https://github.com/googleapis/google-cloud-python/blob/main/.github/workflows/import-profiler.yml)
* Script: [`ci/run_single_test.sh`](https://github.com/googleapis/google-cloud-python/blob/main/ci/run_single_test.sh)