chore: update requirements.txt to address dependabot security alerts. (#1936)

[gcf-owl-bot[bot]]

Created by running: pip-compile requirements.in --generate-hashes --upgrade within synthtool/gcp/templates/java_library/.kokoro and synthtool/docker/owlbot/java/src/ Source-Link: https://github.com/googleapis/synthtool/commit/853dbcd49ea3598fd896007dc48dc97175ee88f1 Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:084ad4c60551b075846bcb2405ec1c14b0d00ec1eb5503d4dd0d2a92cdc2d3e2