[Snyk] Security upgrade postgres from 12.0-alpine to 12.21-alpine

[jeremyjohns10]

Snyk has created this PR to fix 5 vulnerabilities in the dockerfile dependencies of this project.

Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image.

Snyk changed the following file(s):

• docker/Dockerfile.db

We recommend upgrading to postgres:12.21-alpine, as this image has only 0 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Vulnerabilities that will be fixed with an upgrade:

	Issue	Score
	Out-of-bounds Read SNYK-ALPINE310-APKTOOLS-1534688	714
	Use After Free SNYK-ALPINE310-LIBXSLT-503006	614
	Integer Overflow or Wraparound SNYK-ALPINE310-OPENSSL-1075741	614
	Improper Certificate Validation SNYK-ALPINE310-OPENSSL-1089244	614
	NULL Pointer Dereference SNYK-ALPINE310-OPENSSL-587954	614

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• Check the changes in this PR to ensure they won't cause issues with your project.
• Max score is 1000. Note that the real score may have changed since the PR was raised.
• This PR was automatically created by Snyk using the credentials of a real user.

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Learn how to fix vulnerabilities with free interactive lessons:

🦉 NULL Pointer Dereference
🦉 Use After Free