Fix `branches_sharing_code` suggests misleadingly when in assignment

[profetia]

Closes rust-lang/rust-clippy#15004

The lint will note the end suggestion probably needs some adjustments to use the expression result correctly when the expr's is not unit. So I extend this note to also appear when the expr is in an assignment.

changelog: [branches_sharing_code] fix misleading suggestions when in assignment

[rustbot]

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