Use preview builds for testing

[tdstein]

These failures stem from this change in Connect: https://github.com/posit-dev/connect/commit/88ce4ff4d46ae1c4ba831e99b0136d86c0718cf3#diff-db146a204844f1dd26bd7bcafabfbd64d399001dd8bad4e7174611c628a8bfbe

It removed the Justfile commands that this CI uses (just test-rsconnect-python-repo).

The original intention was to ensure that changes to rsconnect-python would not break Connect's CI, which does the inverse operation. It pulls reconnect-python and uses it for its own test matrix. I think a better approach would be what we did with posit-sdk-py and use Docker to run against the preview version of Connect.

[aronatkins]

Ugh. Sorry. Those targets lacked breadcrumbs linking their use to this repository. I thought they were obsolete targets orphaned by some earlier cleanup.

Feel free to temporarily add them back, if that would help.

Agreed that it is better to use preview builds.

[edavidaja]

The relevant code upstream has been restored.