fix(cli-integ): hardcoded qualifier and toolkit stack name in cdk diff with large changeset... test

[iliapolo]

When these are hardcoded, it makes the test less stable in case of potential cleanup failures. For example, canary runs now exhibit this error:

ailed resources:
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751 | custom-stack2 \| 4:57:43 AM \| CREATE_FAILED        \| AWS::S3::Bucket            \| StagingBucket Resource handler returned message: "cdk-abc1111-assets-222461455105-us-east-1 already exists (Service: S3, Status Code: 0, Request ID: null)" (RequestToken: 98d6b74c-97d6-2b80-9e9f-a4d4eb550e2b, HandlerErrorCode: AlreadyExists)
752 | ❌  Environment aws://222461455105/us-east-1 failed bootstrapping: _ToolkitError: The stack named custom-stack2 failed creation, it may need to be manually deleted from the AWS console: ROLLBACK_COMPLETE: Resource handler returned message: "cdk-abc1111-assets-222461455105-us-east-1 already exists (Service: S3, Status Code: 0, Request ID: null)" (RequestToken: 98d6b74c-97d6-2b80-9e9f-a4d4eb550e2b, HandlerErrorCode: AlreadyExists)
753 | at FullCloudFormationDeployment.monitorDeployment (/tmp/tmpcdkXE8YYD/node_modules/aws-cdk/lib/index.js:140591:17)
754 | at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
755 | at async _BootstrapStack.update (/tmp/tmpcdkXE8YYD/node_modules/aws-cdk/lib/index.js:172482:21)
756 | at async /tmp/tmpcdkXE8YYD/node_modules/aws-cdk/lib/index.js:333085:29 {
757 | type: 'toolkit',
758 | source: 'toolkit',
759 | cause: undefined
760 | }

I cleaned up the environment, but lets also make the test create a unique stack every time it runs.

[iliapolo]

Exempting because this keeps getting sporadic failures on a single, but different, test. I am continuing to stabilize tests.