Update tree-sitter requirement from 0.20 to 0.21

Updates the requirements on [tree-sitter](https://github.com/tree-sitter/tree-sitter) to permit the latest version.
- [Release notes](https://github.com/tree-sitter/tree-sitter/releases)
- [Changelog](https://github.com/tree-sitter/tree-sitter/blob/master/CHANGELOG.md)
- [Commits](tree-sitter/tree-sitter@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: tree-sitter
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -20,5 +20,5 @@ incremental = false
 tree-sitter-c = "0.20"
 
 [dependencies]
-tree-sitter = "0.20"
+tree-sitter = "0.21"
 tree-sitter-traversal = "0.1"