fix: Fix markdown horizontal ruler sometimes being treated as a heading

Author: Veykril

src/tools/rust-analyzer/crates/ide/src/hover.rs

@@ -346,7 +346,7 @@ fn hover_offset(
         .unique()
         .reduce(|mut acc: HoverResult, HoverResult { markup, actions }| {
             acc.actions.extend(actions);
-            acc.markup = Markup::from(format!("{}\n---\n{markup}", acc.markup));
+            acc.markup = Markup::from(format!("{}\n\n---\n{markup}", acc.markup));
             acc
         })
         .map(|mut res: HoverResult| {

src/tools/rust-analyzer/crates/ide/src/hover/tests.rs

@@ -303,6 +303,7 @@ m!(ab$0c);
             ---
 
             Outer
+
             ---
 
             ```rust
@@ -4401,6 +4402,7 @@ fn main() {
             ---
 
             size = 8, align = 8, niches = 1
+
             ---
 
             ```rust
@@ -10094,6 +10096,7 @@ fn bar() {
             ```rust
             let field: i32
             ```
+
             ---
 
             ```rust
@@ -10128,6 +10131,7 @@ fn bar() {
             ---
 
             size = 4, align = 4
+
             ---
 
             ```rust