[1.6.x] Fixed #23955 -- Corrected formset fields in topic guide.

Backport of f0c7a6f36005d489e049236922abe0bd3a3eac2c from master
[1.6.x] Corrected example in Form.has_changed() docs.

Backport of ebfadb808043c689b19cfee818c10f63866ee8fc from master