chore: switch cli-integ-testing package to stable (#25131)

The scripts that install the testing package expect it to have a version number that is stable, but because its stability is `experimental` it gets the alpha version treatment.

Error during pipeline build:

```
npm ERR! notarget No matching version found for @aws-cdk-testing/[email protected].
npm ERR! notarget In most cases you or one of your dependencies are requesting
```

But the actual version in the repository is:

```
2.74.0-alpha.999
```

----

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

Author: rix0rrr

packages/@aws-cdk-testing/cli-integ/README.md

@@ -3,13 +3,7 @@
 
 ---
 
-![cdk-constructs: Experimental](https://img.shields.io/badge/cdk--constructs-experimental-important.svg?style=for-the-badge)
-
-> The APIs of higher level constructs in this module are experimental and under active development.
-> They are subject to non-backward compatible changes or removal in any future version. These are
-> not subject to the [Semantic Versioning](https://semver.org/) model and breaking changes will be
-> announced in the release notes. This means that while you may use them, you may need to update
-> your source code when upgrading to a newer version of this package.
+![cdk-constructs: Stable](https://img.shields.io/badge/cdk--constructs-stable-success.svg?style=for-the-badge)
 
 ---
 

packages/@aws-cdk-testing/cli-integ/package.json

@@ -66,8 +66,8 @@
   "engines": {
     "node": ">= 14.15.0"
   },
-  "stability": "experimental",
-  "maturity": "experimental",
+  "stability": "stable",
+  "maturity": "stable",
   "publishConfig": {
     "tag": "latest"
   }