rules:changes and rules:exists list length error messages are wrong

Summary

When adding more than 50 items to a rules:changes or rules:exists, an incorrect and misleading error message noting "maximum is 50 characters" is returned.

This leads users to believe that entries in the list cannot be more than 50 characters long, instead of correctly communicating that the list length itself is limited to 50 elements.

Steps to reproduce

Create a job with rules:changes or rules:exists populated by 51 or more elements.

What is the current bug behavior?

Linting will produce the error jobs:theJobName:rules:rule changes is too long (maximum is 50 characters)

What is the expected correct behavior?

Linting will produce the error jobs:theJobName:rules:rule changes is too long (maximum is 50 elements)

Implementation plan

• rules:changes rule_spec.rb
• rules:exists rule_spec.rb