Fixed leaked container in NamedVolumesVhdSessionRecovery causing test failures in OpenContainer

[OneBlue]

Summary of the Pull Request

This change fixes a leaked container in the NamedVolumesVhdSessionRecovery test case. If the first character of the container ID collided with the one that OpenContainer() creates, this would create a test failure du to an ambiguous prefix

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

Fixes a WSLC Windows test leak in NamedVolumesVhdSessionRecovery that could leave a container behind and interfere with later OpenContainer()-related test behavior.

Changes:

• Add a scope-exit cleanup in NamedVolumesVhdSessionRecovery to prune containers at the end of the test.
• Minor formatting adjustment (blank line) in the test method.