Revert "test: disable MultipleEnvironmentsPerIsolate"

This reverts commit 95ab966a74.

Ref: https://github.com/nodejs/node/issues/14206
Ref: https://github.com/nodejs/node/pull/14246
PR-URL: https://github.com/nodejs/node/pull/14749
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

test/cctest/test_environment.cc

@@ -85,7 +85,6 @@ TEST_F(EnvironmentTest, AtExitWithArgument) {
   EXPECT_EQ(arg, cb_1_arg);
 }
 
-/*
 TEST_F(EnvironmentTest, MultipleEnvironmentsPerIsolate) {
   const v8::HandleScope handle_scope(isolate_);
   const Argv argv;
@@ -101,7 +100,6 @@ TEST_F(EnvironmentTest, MultipleEnvironmentsPerIsolate) {
   RunAtExit(*env2);
   EXPECT_TRUE(called_cb_2);
 }
-*/
 
 static void at_exit_callback1(void* arg) {
   called_cb_1 = true;