Revert the libdgal mod once pyogrio fully supports Python 3.14.

Due to an issue with `pyogrio` (a dependency of `geopandas`) not fully supporting Python 3.14 yet, the `pip install` process for `pyogrio` fails which has a side effect of not installing `libdgal-dev` and several other dependencies.

Because `libdgal` is required for some of the tests in `python-bigquery`, we introduce this change to temporarily ensure that `libdgal` is available in the docker container. [See here for the error message](https://github.com/googleapis/testing-infra-docker/pull/499) and additional details.

Once pyogrio fully supports Python 3.14, this update will no longer be needed and this change can/and should be removed. [See here for status of the expected release](https://github.com/geopandas/pyogrio/issues/560#issuecomment-3562297673) for `pyogrio` that should introduce Python 3.14 support.