chore: Bump Rust version to 1.86 (#28021)

Closes #ISSUE

Release Notes:

- N/A

crates/language/src/buffer.rs

@@ -2876,7 +2876,7 @@ impl BufferSnapshot {
             if let Some(range_to_truncate) = indent_ranges
                 .iter_mut()
                 .filter(|indent_range| indent_range.contains(&outdent_position))
-                .last()
+                .next_back()
             {
                 range_to_truncate.end = outdent_position;
             }

crates/language/src/language_registry.rs

@@ -680,7 +680,7 @@ impl LanguageRegistry {
         // `Path.extension()` returns None for files with a leading '.'
         // and no other extension which is not the desired behavior here,
         // as we want `.zshrc` to result in extension being `Some("zshrc")`
-        let extension = filename.and_then(|filename| filename.split('.').last());
+        let extension = filename.and_then(|filename| filename.split('.').next_back());
         let path_suffixes = [extension, filename, path.to_str()];
         let empty = GlobSet::empty();