test: make use of Number.isNaN to test-readfloat.js

PR-URL: #17310
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: hiromoon

test/parallel/test-readfloat.js

@@ -50,7 +50,7 @@ function test(clazz) {
   buffer[1] = 0xff;
   buffer[2] = 0x7f;
   buffer[3] = 0x7f;
-  assert.ok(isNaN(buffer.readFloatBE(0)));
+  assert.ok(Number.isNaN(buffer.readFloatBE(0)));
   assert.strictEqual(3.4028234663852886e+38, buffer.readFloatLE(0));
 
   buffer[0] = 0xab;