Discovered while working on T419576

Linting the OAD example currently raises date format errors due to validation in the built-in oas3-valid-media-example rule. This behavior is similar to the problem described under oas3-valid-schema-example (line 621 and others) in T414974:

The linter converts dates in YAML to date-time under the hood. If the field that got converted is a date, then the linter reports an error. It's a common behavior (Swagger Editor does that too), but it seems incorrect. You can test this by comparing the schema for startDate and endDate parameters in the YAML input with the same parameters in Linter Results after running the linter.

Investigate whether this validation is working correctly and if we can fix it in the same way as in T414974 - by disabling the rule - or if we need a different solution.