[Snyk] Security upgrade ruby from 3.1.2 to 3.1

[snyk-bot]

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

• Dockerfile

We recommend upgrading to ruby:3.1, as this image has only 240 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
	714	Exposure of Resource to Wrong Sphere SNYK-DEBIAN11-CURL-3065656	No Known Exploit
	614	Out-of-bounds Write SNYK-DEBIAN11-GIT-3051727	No Known Exploit
	714	Integer Overflow or Wraparound SNYK-DEBIAN11-GIT-3232722	No Known Exploit
	714	Integer Overflow or Wraparound SNYK-DEBIAN11-GIT-3232724	No Known Exploit
	714	Out-of-bounds Read SNYK-DEBIAN11-LIBTASN16-3061097	No Known Exploit

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