Auto merge of #6601 - mdm:fix-unit-args-false-positive, r=camsteffen

Auto merge of #6601 - mdm:fix-unit-args-false-positive, r=camsteffen

Fix false positive for unit_arg lint

Fixes #6447

To avoid false positives don't complain about unit args when they come from a path expression, e.g. a local variable.

**Note:** This is my first contribution to Clippy, so I might have messed up somewhere. Any feedback is welcome and I'm happy to work out any kinks.

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changelog: Do not lint unit arguments when they come from a path expression.