docs(runtime-tests): correct stale "no parallelism" PTY comment

The PTY suite now runs file-parallel (see vitest.pty.config.ts), so the comment
claiming "no parallelism" was wrong. The real constraint is node-pty's forks
pool, not serial execution.

packages/runtime-tests/vite.config.ts

@@ -6,7 +6,7 @@ export default defineConfig({
   test: {
     // chalk disables color in non-TTY envs; force it on so ANSI style bugs don't hide from tests
     env: { FORCE_COLOR: "3" },
-    // PTY tests run separately via vitest.pty.config.ts (they need node-pty, no parallelism, longer timeout)
+    // PTY tests run separately via vitest.pty.config.ts (they need node-pty's forks pool and a longer timeout)
     exclude: ["integration/pty/**", "node_modules/**"],
   },
   lint: {