[MCP] Update rmcp to 0.8.3 (#5542)

Picks up modelcontextprotocol/rust-sdk#497 which fixes #5208 by allowing 204 response to MCP initialize notifications instead of just 202.

codex-rs/Cargo.toml

@@ -153,7 +153,7 @@ ratatui = "0.29.0"
 ratatui-macros = "0.6.0"
 regex-lite = "0.1.7"
 reqwest = "0.12"
-rmcp = { version = "0.8.2", default-features = false }
+rmcp = { version = "0.8.3", default-features = false }
 schemars = "0.8.22"
 seccompiler = "0.5.0"
 sentry = "0.34.0"