CI failures due to workflow changes on Connect

[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.