Rewrap the testing module comment

src/testing/index.ts

@@ -1,7 +1,7 @@
 // Test support: the current user's IDs, a fresh temporary directory, the
-// inherited environment, and a plain command runner. It imports no source module, so the repository-level
-// tests in tests/, which reach src/ only through `#testing`, never touch
-// internals.
+// inherited environment, and a plain command runner. It imports no source
+// module, so the repository-level tests in tests/, which reach src/ only
+// through `#testing`, never touch internals.
 import { spawn } from "node:child_process";
 import { once } from "node:events";
 import { mkdtemp } from "node:fs/promises";