Fix parareal convergence monitoring

Issue/feature addressed

Fix bug in Parareal driver related to convergence monitoring. The bug only affect the error norms calculation, not the solution itself. However, the observed difference is minor in most cases.

Proposed solution

Implementation

Tests

Suggested reviewers

Please suggest any people who would be appropriate to review your code.

Notes

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Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).