search_schema() fails to handle array of items gracefully

[tapastro]

In trying to search for keywords in each of the schemas present in the jwst repo, I found that DataModel.search_schema() fails on the wavelengthrange schema here during the walk_schema. I don't know if this is an issue with the schema itself or not, but if the schema is allowed to be written as-is, the method needs updating to allow for a search against a schema with this structure.

I had luck with modifying this line to resemble this line, but I don't know enough about the possible recursions to know if this is the correct fix.