fix: Pruning cron jobs should forbid concurrency

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Pull Request Template

Description

If pruning cron jobs have misconfigured timeouts/schedules they have an opportunity to run concurrently. We should forbid that.

Type of change

Please select the type of change your PR introduces:

• Bugfix
• Feature
• Code Style Update (formatting, renaming)
• Refactor (code changes that do not fix a bug or add a feature)
• Documentation Update
• Other (please describe):

How Has This Been Tested?

Unit tests

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.