test: improve fs.exists coverage

By adding a test case using a path with illegal protocol

PR-URL: https://github.com/nodejs/node/pull/14301
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/parallel/test-fs-exists.js

@@ -23,6 +23,7 @@
 const common = require('../common');
 const assert = require('assert');
 const fs = require('fs');
+const { URL } = require('url');
 const f = __filename;
 
 fs.exists(f, common.mustCall(function(y) {
@@ -33,5 +34,9 @@ fs.exists(`${f}-NO`, common.mustCall(function(y) {
   assert.strictEqual(y, false);
 }));
 
+fs.exists(new URL('https://foo'), common.mustCall(function(y) {
+  assert.strictEqual(y, false);
+}));
+
 assert(fs.existsSync(f));
 assert(!fs.existsSync(`${f}-NO`));