frame pallet macro: fix span for error on wrong returned type. (#5580)
Explicitly give the types in some generated code so that the error shows
up good when user code is wrong.
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Co-authored-by: 
Bastian Köcher <[email protected]>
Explicitly give the types in some generated code so that the error shows
up good when user code is wrong.
---------
Co-authored-by: Bastian Köcher <[email protected]>