Fix bugs with `getRole` and `getElementType`

[khiga8]

We noticed a few unexpected behavior with the latest eslint-plugin-github 4.9.0 release, which all seems to stem from using getPropValue instead of getLiteralPropValue in our methods getElementType and getRole.

getElementType will return a div for the following. It should instead return Box and not try to assess the conditional.

<Box as={isNavigationOpen ? 'div' : 'nav'} />

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getRole will return a "generic" here. I don't think it should return anything.

<Box role={isNavigationOpen ? 'generic' : 'navigation'} />

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getRole will return a "role" here. It should retur undefined since this is role is set to a variable.

<Box role={role} />

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This PR:

• adds test which initially fail to reflect the failures we observed
• adds fix for test which is to swap getPropValue with getLiteralPropValue.