[significant_drop_tightening] Ignore inexpensive statements
Not all statements that follow the last use of a lock guard are expensive and can therefore be ignored by the lint.
```rust
pub fn foo() -> i32 {
let mutex = Mutex::new(1);
let lock = mutex.lock().unwrap();
let rslt = *lock;
let another = rslt;
another
}
```
---
changelog: [`significant_drop_tightening`]: No longer lints for inexpensive statements after the lock guard
[#10363](https://github.com/rust-lang/rust-clippy/pull/10363)
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