TEST: Fix drop tests for older Rust

In the test, test with Vec first to see how Rust implements panic
recovery while elements drop. If Vec drops all the elements, then we
test that arrayvec does too.

tests/tests.rs

@@ -127,7 +127,22 @@ fn test_drop_panics() {
             }
         }
     }
+    // check if rust is new enough
+    flag.set(0);
+    {
+        let array = vec![Bump(flag), Bump(flag)];
+        let res = catch_unwind(AssertUnwindSafe(|| {
+            drop(array);
+        }));
+        assert!(res.is_err());
+    }
 
+    if flag.get() != 2 {
+        println!("test_drop_panics: skip, this version of Rust doesn't continue in drop_in_place");
+        return;
+    }
+
+    flag.set(0);
     {
         let mut array = ArrayVec::<[Bump; 128]>::new();
         array.push(Bump(flag));