Rollup merge of #77559 - camelid:fix-rustdoc-warnings-invalid-rust-syntax, r=lcnr

Fix rustdoc warnings about invalid Rust syntax

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -38,13 +38,13 @@ pub struct OpaqueTypeDecl<'tcx> {
     /// then `substs` would be `['a, T]`.
     pub substs: SubstsRef<'tcx>,
 
-    /// The span of this particular definition of the opaque type.  So
+    /// The span of this particular definition of the opaque type. So
     /// for example:
     ///
-    /// ```
+    /// ```ignore (incomplete snippet)
     /// type Foo = impl Baz;
     /// fn bar() -> Foo {
-    ///             ^^^ This is the span we are looking for!
+    /// //          ^^^ This is the span we are looking for!
     /// ```
     ///
     /// In cases where the fn returns `(impl Trait, impl Trait)` or