Fix the type argument on the deep flattening spread test.

Change-Id: Icba0904c88a18901c0a2d423a8ce7ab7af8413fd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/94941
Reviewed-by: Leaf Petersen <leafp@google.com>
Commit-Queue: Bob Nystrom <rnystrom@google.com>

tests/language_2/spread_collections/const_test.dart

@@ -50,7 +50,8 @@ void testList() {
 
   // Does not deep flatten.
   Expect.identical(
-      const <int>[1, 2, <int>[3], 4], const <int>[1, ...<int>[2, <int>[3], 4]]);
+      const <Object>[1, 2, <int>[3], 4],
+      const <Object>[1, ...<Object>[2, <int>[3], 4]]);
 
   // Establishes const context.
   Expect.identical(const <Symbol>[Symbol("sym")],

tests/language_2/spread_collections/spread_test.dart

@@ -51,7 +51,8 @@ void testList() {
   // Does not deep flatten.
   var innerList = <int>[3];
   Expect.listEquals(
-      <int>[1, 2, innerList, 4], <int>[1, ...<int>[2, innerList, 4]]);
+      <Object>[1, 2, innerList, 4],
+      <Object>[1, ...<Object>[2, innerList, 4]]);
 
   // Downcast element.
   Expect.listEquals(list, <int>[...<num>[1, 2, 3, 4]]);