Pass pty correctly in modal shell <task-id>

[aksh-at]

Since exec is decorated with @click.command and we're calling it directly here, pty was getting a weird default value (typer.OptionInfo).

Backward/forward compatibility checks

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Check these boxes or delete any item (or this section) if not relevant for this PR.

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Note on protobuf: protobuf message changes in one place may have impact to
multiple entities (client, server, worker, database). See points above.

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Changelog

[mwaskom]

Probably could refactor this a little better at some point.