tools: use arrow function for callback in lint-sh.js

The function declaration inside an else block is odd (and violates a
recommended ESLint rule). We tend to use arrow functions for callbacks
anyway, so switch to that.

PR-URL: #41256
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/lint-sh.js

@@ -166,11 +166,11 @@ if (
   const entryPoint = resolve(process.argv[2]);
   const stats = statSync(entryPoint, { throwIfNoEntry: false });
 
-  function onError(e) {
+  const onError = (e) => {
     console.log(USAGE_STR);
     console.error(e);
     process.exitCode = 1;
-  }
+  };
   if (stats?.isDirectory()) {
     SPAWN_OPTIONS.cwd = entryPoint;
     checkFiles(...findScriptFilesRecursively(entryPoint)).catch(onError);