test: refactor flag check

Refactor test-vm-run-in-new-context so that check for `--expose-gc` flag
will not run afoul of an upcoming lint rule that checks that string
literals are not used for the `message` argument of
`assert.strictEqual()`.

Backport-PR-URL: #22888
PR-URL: #22849
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-vm-run-in-new-context.js

@@ -26,8 +26,8 @@ const common = require('../common');
 const assert = require('assert');
 const vm = require('vm');
 
-assert.strictEqual(typeof global.gc, 'function',
-                   'Run this test with --expose-gc');
+if (typeof global.gc !== 'function')
+  assert.fail('Run this test with --expose-gc');
 
 common.globalCheck = false;