refactor: fix retry behaviour in tedge_flows.robot

[jarhodes314]

Proposed changes

Modify the tests in tedge_flows.robot so retries are handled correctly.

For example, this failure shows a Directory not empty error when we retried the test: https://github.com/thin-edge/thin-edge.io/actions/runs/25811734528/job/75832244151. This is due to the directory not being cleaned-up at the end of the test, so the retry tries to install the already-installed flow and fails at that point.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s. You can activate automatic signing by running just prepare-dev once)
• I ran just format as mentioned in CODING_GUIDELINES
• I used just check as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
912	0	4	912	100	2h37m10.950313999s