chore(cdk-build-tools): temporarily disable feature flag test (#12711)

This was originally introduced in 31b1b32.

However, the forward merge of this change onto the v2-main branch is
failing unit tests in consuming modules that implicitly
depend on the future flag's behaviour. 
For example, unit tests in the `aws-s3` module depend on the
behaviour of the `@aws-cdk/aws-kms:defaultKeyPolicies` flag.

Temporarily disable this feature until these can be resolved.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

tools/cdk-build-tools/lib/feature-flag.ts

@@ -30,9 +30,9 @@ export function testFutureBehavior<T>(
 
   const major = cdkMajorVersion(repoRoot);
   if (major === 2) {
-    // In CDKv2, the default behaviour is as if the feature flags are enabled. So, ignore the feature flags passed.
-    const app = new cdkApp();
-    return test(name, async () => fn(app));
+    // Temporaily disable CDKv2 behaviour
+    // const app = new cdkApp();
+    // return test(name, async () => fn(app));
   }
   const app = new cdkApp({ context: flags });
   return test(name, () => fn(app));
@@ -59,8 +59,8 @@ export function testLegacyBehavior<T>(
 
   const major = cdkMajorVersion(repoRoot);
   if (major === 2) {
-    // In CDKv2, legacy behaviour is not supported. Skip the test.
-    return;
+    // Temporarily disable CDKv2 behaviour
+    // return;
   }
   const app = new cdkApp();
   return test(name, () => fn(app));