Fix inclusion validation for CI entries

What does this MR do and why?

As we realized in !101350 (merged):

We have the "inclusion" validation for the when keyword but no validation for its type. So, the attribute also accepts an array as the value. The "inclusion" validation of ActiveModel::Validations also accepts array values and compares each element.

We fixed that problem in that MR for the Entry::Job and Entry::Bridge entries. In this issue, we fix the following entries by specifying the type along with the inclusion validation:

• Entry::Artifacts
• Entry::Cache

Screenshots or screen recordings

• Example: Entry::Artifacts

Before fix (validation passes):

After fix:

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #378368 (closed)