Fix virtual environment reuse error in multi-deployment jobs

[jamiezieziula]

Problem

When this action runs multiple times in the same GitHub Actions job, subsequent runs fail with:

error: Failed to create virtual environment
  Caused by: A virtual environment already exists at .venv

This causes intermittent failures when deploying multiple Prefect flows in the same workflow job.

Root Cause

The uv venv command (line 55) creates a .venv directory but doesn't clean it up. When called a second time in the same job, it refuses to overwrite the existing directory without the --clear flag.

This became an issue after v4.3.0 re-enabled uv for dependency management (PR #66).

Solution

Add --clear flag to uv venv command:

- name: Set up environment
  run: uv venv --clear  # Forces recreation if exists
  shell: bash

Testing

Tested by running action multiple times in same job - second run now succeeds instead of failing.

Impact

• ✅ No breaking changes - behavior identical for first-time runs
• ✅ Fixes intermittent failures in multi-deployment workflows
• ✅ Eliminates need for cleanup workarounds in consuming repos
• ✅ Aligns with uv best practices for CI environments

Related

• Fixes failures in PrefectHQ/flows workflows
• Allows removal of cleanup workarounds added in PrefectHQ/flows#2407