Improve spec geo_site_form_spec.js

What does this MR do and why?

This MR addresses the following comment:

• @cngo started a discussion: (+1 comment)

  I think we generally avoid updating store state like this as it's similar to doing setData after component creation. WDYT about passing in the state to createComponent to initialise the store there? This way we can improve the test code even more while we're here

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Related to #417642 (closed)