Non-breaking spaces in stack-policy example JSON.

[matthewhembree]

File: https://github.com/awsdocs/aws-cloudformation-user-guide/blob/main/doc_source/protect-stack-resources.md

Has NBSP in the example JSON which if copy pasted exactly will not work.

This might affect other snippets, I'm just doing one file. Project admins should consider auditing the snippets.

. Thanks!