Reduce runtime of slow test (#4946)

Author: ngoldbaum

src/types/mappingproxy.rs

@@ -539,7 +539,7 @@ mod tests {
     #[test]
     fn iter_mappingproxy_nosegv() {
         Python::with_gil(|py| {
-            const LEN: usize = 10_000_000;
+            const LEN: usize = 1_000;
             let items = (0..LEN as u64).map(|i| (i, i * 2));
 
             let dict = items.clone().into_py_dict(py).unwrap();
@@ -551,7 +551,7 @@ mod tests {
                 let i: u64 = k.extract().unwrap();
                 sum += i;
             }
-            assert_eq!(sum, 49_999_995_000_000);
+            assert_eq!(sum, 499_500);
         })
     }
 }