fmt and fix lint

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -83,7 +83,7 @@ pub fn retain(&mut self, tags: &FxHashSet<BorTag>) {
         self.borrows.truncate(write_idx);
 
         #[cfg(not(feature = "stack-cache"))]
-        drop(first_removed); // This is only needed for the stack-cache
+        let _unused = first_removed; // This is only needed for the stack-cache
 
         #[cfg(feature = "stack-cache")]
         if let Some(first_removed) = first_removed {

src/tools/miri/tests/fail/uninit_buffer_with_provenance.rs

@@ -1,7 +1,6 @@
 //@error-in-other-file: memory is uninitialized at [0x4..0x8]
 //@normalize-stderr-test: "a[0-9]+" -> "ALLOC"
 #![feature(strict_provenance)]
-
 #![allow(drop_copy)]
 
 // Test printing allocations that contain single-byte provenance.