[Snyk] Security upgrade ubuntu from latest to kinetic

[circleci-secops]

This PR was automatically created by Snyk using the credentials of a real user.

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

Changes included in this PR

• docs/examples/apt-cacher-ng.Dockerfile

We recommend upgrading to ubuntu:kinetic, as this image has only 7 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Some of the most important vulnerabilities in your base image include:

Severity	Priority Score / 1000	Issue	Exploit Maturity
	150	Out-of-bounds Write SNYK-UBUNTU2204-BASH-3098342	No Known Exploit
	221	Improper Certificate Validation SNYK-UBUNTU2204-OPENSSL-5296052	No Known Exploit
	221	Improper Certificate Validation SNYK-UBUNTU2204-OPENSSL-5296082	No Known Exploit
	221	CVE-2023-29383 SNYK-UBUNTU2204-SHADOW-5425688	No Known Exploit
	221	CVE-2023-29383 SNYK-UBUNTU2204-SHADOW-5425688	No Known Exploit

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