Fix `set-contains-or-insert` FP when set is mutated before `insert`

[profetia]

Closes rust-lang/rust-clippy#15990

changelog: [set-contains-or-insert] fix FP when set is mutated before insert

[rustbot]

r? @Jarcho

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[profetia]

r? clippy

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[profetia]

Sorry I must have forgotten (´･ω･`). I've added them now