fix: Dont assume ascii in remove_markdown

Fixes rust-lang#16142

Author: Waqar144

crates/ide/src/markdown_remove.rs

@@ -25,7 +25,10 @@ pub(crate) fn remove_markdown(markdown: &str) -> String {
         }
     }
 
-    if let Some(p) = out.rfind(|c| c != '\n') {
+    if let Some(mut p) = out.rfind(|c| c != '\n') {
+        while !out.is_char_boundary(p + 1) {
+            p += 1;
+        }
         out.drain(p + 1..);
     }
 
@@ -153,4 +156,10 @@ book] or the [Reference].
 
             For more information on the various types of functions and how they're used, consult the Rust book or the Reference."#]].assert_eq(&res);
     }
+
+    #[test]
+    fn on_char_boundary() {
+        expect!["a┘"].assert_eq(&remove_markdown("```text\na┘\n```"));
+        expect!["وقار"].assert_eq(&remove_markdown("```\nوقار\n```\n"));
+    }
 }