Update tree-sitter-c requirement from 0.20 to 0.21

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

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

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

Cargo.toml

@@ -17,7 +17,7 @@ debug = 0
 incremental = false
 
 [dev-dependencies]
-tree-sitter-c = "0.20"
+tree-sitter-c = "0.21"
 
 [dependencies]
 tree-sitter = "0.20"