🐛 remove 3 backticks messing the hover (#12273)

# Description

The hover was bugged with 3 backticks. I don't understand how it worked
before, but this apparently now works correctly on my machine. This is
really puzzling. My next step is to make a test to assert this will
break a little less. I fixed it 3 times in the past

# Tests + Formatting

Added a test to be sure this doesn't breaks again 😄 (at least from
nushell/nushell side)

src/ide.rs

@@ -211,8 +211,7 @@ pub fn hover(engine_state: &mut EngineState, file_path: &str, location: &Value)
         Some((Id::Declaration(decl_id), offset, span)) => {
             let decl = working_set.get_decl(decl_id);
 
-            //let mut description = "```\n### Signature\n```\n".to_string();
-            let mut description = "```\n".to_string();
+            let mut description = String::new();
 
             // first description
             description.push_str(&format!("{}\n", decl.usage()));