(cli): `cdk ls` should work even when `cdk deploy` is in progress

### Describe the feature

I think `cdk ls` should work, even when there's already a deployment in progress.

### Use Case

It's pretty typical to work across tabs and sometimes I want to `ls` while _another_ process is already busy doing a deploy.

### Proposed Solution

When running `ls` change `--output` value to some `/tmp/*` dir.

### Other Information

Get an error when doing an `ls` while `deploy` is running:

> Other CLIs (PID=81799) are currently reading from cdk.out. Invoke the CLI in sequence, or use '--output' to synth into different directories.

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2.171.0

### Environment details (OS name and version, etc.)

macOS

Start at the implementation of `cdk ls` and its handling of `--output`, then compare how `cdk deploy` uses `cdk.out` while another process is active. Done means `cdk ls` succeeds during a deployment without interfering with the deployment's output directory.

Written by the indexing model from the issue text.