chore(assertions): explicit feature flags to produce a consistent tem…

…plate during tests (#15924)

In v1, the default value of the `@aws-cdk/core:newStyleStackSynthesis` flag is `false`. As a consequence, `Template.fromStack()` generates, by default, a template without the rule and parameter related to bootstrap versions. In v2,  the default value of this flag is `true`. So this test fails in the v2 branch. By explicitly setting the flag to `false`, we ensure that the tests passes on both v1 and v2, regardless of the default values.

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packages/@aws-cdk/assertions/test/template.test.ts

@@ -1,4 +1,4 @@
-import { CfnResource, Stack } from '@aws-cdk/core';
+import { App, CfnResource, Stack } from '@aws-cdk/core';
 import { Construct } from 'constructs';
 import { Match, Template } from '../lib';
 
@@ -25,7 +25,12 @@ describe('Template', () => {
     });
 
     test('fromStack', () => {
-      const stack = new Stack();
+      const app = new App({
+        context: {
+          '@aws-cdk/core:newStyleStackSynthesis': false,
+        },
+      });
+      const stack = new Stack(app);
       new CfnResource(stack, 'Foo', {
         type: 'Foo::Bar',
         properties: {