chore(python): update dependencies in .kokoro/requirements.txt (#397)

Source-Link: googleapis/synthtool@e3a1277
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:452901c74a22f9b9a3bd02bce780b8e8805c97270d424684bff809ce5be8c2a2

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

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,4 +13,4 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:7a40313731a7cb1454eef6b33d3446ebb121836738dc3ab3d2d3ded5268c35b6
+  digest: sha256:452901c74a22f9b9a3bd02bce780b8e8805c97270d424684bff809ce5be8c2a2