Fix clippy lint in new rustc nightly

New nightly lint warning "called `Iterator::last` on a
`DoubleEndedIterator`; this will needlessly iterate the entire iterator"

Code that gives the warning is correct, allow the lint to remove the
warning.

Update rustc nightly to 2025-01-16

bitcoin/src/taproot/merkle_branch.rs

@@ -252,6 +252,7 @@ impl Iterator for IntoIter {
     fn nth(&mut self, n: usize) -> Option<Self::Item> { self.0.nth(n) }
 
     #[inline]
+    #[allow(clippy::double_ended_iterator_last)] // False positive.  Using `.last()` on a `vec::IntoIter` is correct.
     fn last(self) -> Option<Self::Item> { self.0.last() }
 
     #[inline]

nightly-version

@@ -1 +1 @@
-nightly-2025-01-10
+nightly-2025-01-16