Automate submodule updates

[andrewpollock]

Describe the bug Git submodules aren't routinely updated, notably the OSV Schema

To Reproduce Steps to reproduce the behaviour:

$ git submodule status
 88e5ae3c40c85b702ba89a34c29f233048abb12b docker/worker/osv-test (v0.2-4-g88e5ae3)
 b241bbc1ad920771707fe03e4cedd4e8c492e143 gcp/api/googleapis (common-protos-1_3_1-3027-gb241bbc1a)
 21c7653f2e948af769618c3b91b94a54d2935ac1 osv/osv-schema (v1.6.0)

(v1.6.3 is the latest release)

Expected behaviour The OSV Schema in particular tracks the latest released version

Additional context

• https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#package-ecosystem
• https://docs.renovatebot.com/modules/manager/git-submodules/

[github-actions[bot]]

This issue has not had any activity for 60 days and will be automatically closed in two weeks

See https://github.com/google/osv.dev/blob/master/CONTRIBUTING.md for how to contribute a PR if you're interested in helping out.