Fix .within operator in nonCompountAttStmt

[CDDL][1] defines that:

>A map matches a specification given as a group when the group matches
>a sequence of name/value pairs such that all of these name/value
>pairs are present in the map and the map has no name/value pair that
>is not covered by the group.

Therefore the control `.within { fmt: text .ne "compound" }` forbids any maps
that contain additional fields besides `fmt`, which is clearly not what was
intended.

[1]: https://datatracker.ietf.org/doc/html/rfc8610#section-2.1

index.bs

@@ -6933,7 +6933,7 @@ The "compound" attestation statement format is used to pass multiple, self-conta
                           attStmt: [2* nonCompoundAttStmt]
                       )
 
-    nonCompoundAttStmt = { $$attStmtType } .within { fmt: text .ne "compound" }
+    nonCompoundAttStmt = { $$attStmtType } .within { fmt: text .ne "compound", * any => any }
     ```
 
 : Signing procedure