doc: add missing setEncoding call in ESM example

Adding `setEncoding()` ensures that the example handles characters
split across chunk boundaries well.

PR-URL: nodejs#47558
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Moshe Atlow <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Harshitha K P <[email protected]>
Reviewed-By: Rafael Gonzaga <[email protected]>

doc/api/esm.md

@@ -1036,6 +1036,7 @@ export function load(url, context, nextLoad) {
     return new Promise((resolve, reject) => {
       get(url, (res) => {
         let data = '';
+        res.setEncoding('utf8');
         res.on('data', (chunk) => data += chunk);
         res.on('end', () => resolve({
           // This example assumes all network-provided JavaScript is ES module