test(bootstrapper): prevent unintended background downloads

[booxter]

Pull Request Description

What

Tests replacing PrepareSource.run() do not consume background results.
Disable background work too so placeholder URLs never trigger requests.

Why

This becomes important in sandboxed environments where network requests
don't quickly return an error but instead go into a backoff retry loop.

• PR follows CONTRIBUTING.md guidelines

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📥 Commits

Reviewing files that changed from the base of the PR and between e724cb4 and 77b7bc7.

📒 Files selected for processing (2)

• tests/test_bootstrapper.py
• tests/test_bootstrapper_iterative.py

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📝 Walkthrough

Walkthrough

Six bootstrapper tests now mock PrepareSource.background_work to return None. The existing PrepareSource.run mock remains in the multiple-version failure-continuation test.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Merge Risk: ⚪ Minimal · up to 77b7b

These test-only stubs prevent background work in the affected tests without changing production behavior. No concrete regression remains identified, so the change appears mergeable subject to normal checks.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: preventing unintended background downloads in bootstrapper tests.
Description check	✅ Passed	The description explains the test change and its purpose. It matches the changeset and PR objectives.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[rd4398]

LGTM! Thanks for the fix

[mergify]

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