fix(misconf): check if metadata is not nil

[nikpivkin]

Description

This PR fixes a potential panic when falling back to embedded checks due to missing annotations.

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[nikpivkin]

@simar7 Hmm, this is the second time today that I've run into problems in CI. Locally, the new test passes successfully, but in Github Actions the test fails with an error: could not find schema “fooschema”, even though the Rego check in the test doesn't even use schemas.