chore: update requirements.txt to address dependabot security alerts.

[zhumin8]

Created by running: pip-compile requirements.in --generate-hashes --upgrade within synthtool/gcp/templates/java_library/.kokoro and synthtool/docker/owlbot/java/src/

This should resolve alerts: https://github.com/googleapis/synthtool/security/dependabot/59 https://github.com/googleapis/synthtool/security/dependabot/56 https://github.com/googleapis/synthtool/security/dependabot/54 https://github.com/googleapis/synthtool/security/dependabot/57 https://github.com/googleapis/synthtool/security/dependabot/53

closes #1932 closes #1915 closes #1914