ug_testing.rst: also mention checking the base suite results

[phil-blain]

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  ug_testing.rst: also mention checking the base suite results

In the "End-To-End Testing Procedure" section of the user guide, we instruct users to run a base suite and a test suite, but only mention checking the results of the test suite.

Also mention checking the results of the base suite first, to make sure everything passes before checking the test suite.

Suggested-by: Jean-Francois Lemieux jean-francois.lemieux@canada.ca

[phil-blain]

The rendered doc for that section is here: https://cice-consortium-cice--934.org.readthedocs.build/en/934/user_guide/ug_testing.html#end-to-end-testing-procedure