chore(python): add missing import for prerelease testing (#410)

Source-Link: googleapis/synthtool@d2871d9
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:b2dc5f80edcf5d4486c39068c9fa11f7f851d9568eea4dcba130f994ea9b5e97

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

packages/google-cloud-python-speech/noxfile.py

@@ -19,6 +19,7 @@
 from __future__ import absolute_import
 import os
 import pathlib
+import re
 import shutil
 import warnings