build: upgrade go version to 1.18

[takclark]

GitHub Action tests have been failing since this run. It's caused by dependency on strings.Cut, which was added in 1.18 and appeared in dependency https://github.com/docker/cli some time between v20.10.17 and v24.0.1.

So, go 1.18 is the minimum required version here. This should fix the tests.

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

[takclark]

and you can now see "Nancy" failing on the runc version because of CVE-2024-21626, which I would also like to fix