Add regression test for #9473

Author: GuillaumeGomez

tests/ui/doc/issue_9473.fixed

@@ -0,0 +1,9 @@
+#![warn(clippy::doc_markdown)]
+
+// Should not warn!
+/// Blah blah blah <code>[FooBar]&lt;[FooBar]&gt;</code>.
+pub struct Foo(u32);
+
+// Should warn.
+/// Blah blah blah <code>[FooBar]&lt;[FooBar]&gt;</code>[`FooBar`].
+pub struct FooBar(u32);

tests/ui/doc/issue_9473.rs

@@ -0,0 +1,9 @@
+#![warn(clippy::doc_markdown)]
+
+// Should not warn!
+/// Blah blah blah <code>[FooBar]&lt;[FooBar]&gt;</code>.
+pub struct Foo(u32);
+
+// Should warn.
+/// Blah blah blah <code>[FooBar]&lt;[FooBar]&gt;</code>[FooBar].
+pub struct FooBar(u32);

tests/ui/doc/issue_9473.stderr

@@ -0,0 +1,15 @@
+error: item in documentation is missing backticks
+  --> tests/ui/doc/issue_9473.rs:8:58
+   |
+LL | /// Blah blah blah <code>[FooBar]&lt;[FooBar]&gt;</code>[FooBar].
+   |                                                          ^^^^^^
+   |
+   = note: `-D clippy::doc-markdown` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::doc_markdown)]`
+help: try
+   |
+LL | /// Blah blah blah <code>[FooBar]&lt;[FooBar]&gt;</code>[`FooBar`].
+   |                                                          ~~~~~~~~
+
+error: aborting due to 1 previous error
+