Change remaining "final" to "const" in language/const_syntax_test.

tests/language/const_syntax_test.dart

Index: tests/language/const_syntax_test.dart
diff --git a/tests/language/const_syntax_test.dart b/tests/language/const_syntax_test.dart
index 5853aead776b92d22d62c9264573b4af13c86243..7540709735aafdcec99ff02f1e295c133315f884 100644
--- a/tests/language/const_syntax_test.dart
+++ b/tests/language/const_syntax_test.dart
@@ -3,10 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
-  final f0 = 42;
-  final f1; /// 01: compile-time error
-  final int f2 = 87;
-  final int f3; /// 02: compile-time error
+  const f0 = 42;
+  const f1; /// 01: compile-time error
+  const int f2 = 87;
+  const int f3; /// 02: compile-time error
   Expect.equals(42, f0);
   Expect.equals(87, f2);