Recipe test workflow support recipes in subdirectories

[alistairsellar]

Description

Enables recipe test workflow to run recipes in subdirectories of esmvaltool/recipes

• Closes #3566

• Link to documentation:

• • *

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[alistairsellar]

Hi @ehogan this is the change we discussed on Monday. It runs for me OK on both metoffice and jasmin sites, with one recipe added from a subdirectory. Please could you review?