[Snyk] Security upgrade alpine from 3.20.3 to 3.21.2

[powerman]

Snyk has created this PR to fix 1 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):

• Dockerfile

We recommend upgrading to alpine:3.21.2, 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
	CVE-2024-9143 SNYK-ALPINE320-OPENSSL-8235201	364
	CVE-2024-9143 SNYK-ALPINE320-OPENSSL-8235201	364

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[!IMPORTANT]

• 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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