Rollup merge of #45644 - zackmdavis:edit_disallowed_inner_attr_note, r=estebank

Rollup merge of #45644 - zackmdavis:edit_disallowed_inner_attr_note, r=estebank

edit and fix bad spacing of inner-attribute-not-allowed note

This multiline string literal was missing a backslash, leaving an awkward
newline and 35 spaces in the middle of the message.

But while we're here, the existing message seems kind of long in comparison to
similar notes: to cut it down, we excise the mentions of doc comments, which
seems sensible because we know that this erroneous attribute is not a doc
comment (notice the `is_sugared_doc: false` at the end of the function; if it
had been a doc comment, that error would get set in the `token::DocComment`
match branch of `parse_outer_attributes`).