Add invalid field to SnippetInputAction specs

What does this MR do?

This is a followup MR from !33379 (comment 351765183)

In this MR we check in the specs which field was the culprit of the validation error.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content