doc_paragraphs_missing_punctuation: add a missing period in another test

Author: AudaciousAxiom

tests/ui/blanket_clippy_restriction_lints.rs

@@ -3,7 +3,7 @@
 
 #![warn(clippy::blanket_clippy_restriction_lints)]
 
-//! Test that the whole restriction group is not enabled
+//! Test that the whole restriction group is not enabled.
 #![warn(clippy::restriction)]
 //~^ blanket_clippy_restriction_lints
 #![deny(clippy::restriction)]