docs: Fix casing of "Tree-sitter" (#25427)

This PR fixes the casing of "Tree-sitter" in the docs.

It is "Tree-sitter", not "Tree Sitter" or "Tree-Sitter".

Release Notes:

- N/A

docs/src/languages/cpp.md

@@ -2,7 +2,7 @@
 
 C++ support is available natively in Zed.
 
-- Tree Sitter: [tree-sitter/tree-sitter-cpp](https://github.com/tree-sitter/tree-sitter-cpp)
+- Tree-sitter: [tree-sitter/tree-sitter-cpp](https://github.com/tree-sitter/tree-sitter-cpp)
 - Language Server: [clangd/clangd](https://github.com/clangd/clangd)
 
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