Suggest `return`ing tail expressions in async functions
This PR fixes#92308.
Previously, the suggestion to `return` tail expressions (introduced in #81769) did not apply to `async` functions, as the suggestion checked whether the types were equal disregarding `impl Future<Output = T>` syntax sugar for `async` functions. This PR changes that in order to fix a potential papercut.
I'm not sure if this is the "right" way to do this, so if there is a better way then please let me know.
I amended an existing test introduced in #81769 to add a regression test for this, if you think I should make a separate test I will.
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