Add blank lines after module-level //! comments.

Most modules have such a blank line, but some don't. Inserting the blank
line makes it clearer that the `//!` comments are describing the entire
module, rather than the `use` declaration(s) that immediately follows.

compiler/rustc_pattern_analysis/tests/complexity.rs

@@ -1,4 +1,5 @@
 //! Test the pattern complexity limit.
+
 use common::*;
 use rustc_pattern_analysis::{pat::DeconstructedPat, usefulness::PlaceValidity, MatchArm};
 

compiler/rustc_pattern_analysis/tests/exhaustiveness.rs

@@ -1,4 +1,5 @@
 //! Test exhaustiveness checking.
+
 use common::*;
 use rustc_pattern_analysis::{
     pat::{DeconstructedPat, WitnessPat},

compiler/rustc_pattern_analysis/tests/intersection.rs

@@ -1,4 +1,5 @@
 //! Test the computation of arm intersections.
+
 use common::*;
 use rustc_pattern_analysis::{pat::DeconstructedPat, usefulness::PlaceValidity, MatchArm};