test: address deprecation warning

fs.truncateSync() emits a deprecation warning when called with a file
descriptor. Move to fs.ftruncateSync().

PR-URL: #38448
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/pummel/test-fs-largefile.js

@@ -34,7 +34,7 @@ const fd = fs.openSync(filepath, 'w+');
 const offset = 5 * 1024 * 1024 * 1024; // 5GB
 const message = 'Large File';
 
-fs.truncateSync(fd, offset);
+fs.ftruncateSync(fd, offset);
 assert.strictEqual(fs.statSync(filepath).size, offset);
 const writeBuf = Buffer.from(message);
 fs.writeSync(fd, writeBuf, 0, writeBuf.length, offset);