fix clippy::manual_assert in tests

Author: hellow554

tests/adaptors_no_collect.rs

@@ -43,4 +43,4 @@ fn combinations_no_collect() {
 #[test]
 fn combinations_with_replacement_no_collect() {
     no_collect_test(|iter| iter.combinations_with_replacement(5))
-}
+}

tests/quick.rs

@@ -258,9 +258,7 @@ where
         let mut it = get_it();
 
         for _ in 0..(counts.len() - 1) {
-            if it.next().is_none() {
-                panic!("Iterator shouldn't be finished, may not be deterministic");
-            }
+            assert!(it.next().is_some(), "Iterator shouldn't be finished, may not be deterministic");
         }
 
         if it.next().is_none() {