Throw an error when concatenations have different number of children

[aabills]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes #4561

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• [ ] New feature (non-breaking change which adds functionality)
• [ ] Optimization (back-end change that speeds up the code)
• [x] Bug fix (non-breaking change which fixes an issue)

Key checklist:

• [ ] No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• [ ] All tests pass: $ python run-tests.py --all (or $ nox -s tests)
• [ ] The documentation builds: $ python run-tests.py --doctest (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ python run-tests.py --quick (or $ nox -s quick).

Further checks:

• [ ] Code is commented, particularly in hard-to-understand areas
• [ ] Tests added that prove fix is effective or that feature works

[aabills]

Tests are going to fail on this due to an unrelated issue that I am working on concurrently, so opening this for now and once we merge the other one we can merge this one.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.26%. Comparing base (1022c6b) to head (f313159). Report is 3 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #4562 +/- ## =========================================== - Coverage 99.27% 99.26% -0.02% =========================================== Files 302 302 Lines 22868 22889 +21 =========================================== + Hits 22703 22721 +18 - Misses 165 168 +3 ```

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[kratman]

@aabills Can you update the bug fix section of the change log

[aabills]

@aabills Can you update the bug fix section of the change log

Done, I realized I haven't done that for the other PR's either so I did all 3.