test: allow running with NODE_PENDING_DEPRECATION

Make the test for pending deprecations work when the env var
is set during the whole test suite run.

PR-URL: https://github.com/nodejs/node/pull/18991
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-pending-deprecation.js

@@ -25,7 +25,8 @@ switch (process.argv[2]) {
     break;
   default:
     // Verify that the flag is off by default.
-    assert.strictEqual(config.pendingDeprecation, undefined);
+    const envvar = process.env.NODE_PENDING_DEPRECATION;
+    assert.strictEqual(config.pendingDeprecation, envvar && envvar[0] === '1');
 
     // Test the --pending-deprecation command line switch.
     fork(__filename, ['switch'], {