Replace std::sync::Mutex with parking_lot::Mutex in languages/src/python.rs (#29889)

This appears to be the only place `std::sync::Mutex` is used, Zed always
prefers `parking_lot`.

Release Notes:

- N/A

Cargo.lock

@@ -7992,6 +7992,7 @@ dependencies = [
  "log",
  "lsp",
  "node_runtime",
+ "parking_lot",
  "paths",
  "pet",
  "pet-conda",