Fix incorrect error message

[aabills]

Description

When the parameters dictionary is called with a key of Primary: Some parameter [some unit], pybamm directs the user to use the dimensional version of that parameter. This is inconsequential but I find it annoying.

this PR simply corrects that logic.

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 # (issue)

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)
• 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 -m pytest (or $ nox -s tests)
• The documentation builds: $ python -m pytest --doctest-plus src (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ 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

[kratman]

Seems good

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.21%. Comparing base (72c23ea) to head (864388f).
Report is 25 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4672   +/-   ##
========================================
  Coverage    99.21%   99.21%           
========================================
  Files          302      302           
  Lines        22858    22880   +22     
========================================
+ Hits         22679    22701   +22     
  Misses         179      179           

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[aabills]

added a quick test to hit coverage