Skip test that relies on stringification in lite mode

Stringification depends on the dynamic API, which is unavailable in lite
mode.

Thanks to @kentonv for the wording.

c++/src/capnp/encoding-test.c++

@@ -1667,6 +1667,8 @@ TEST(Encoding, Embeds) {
     checkTestMessage(reader.getRoot<TestAllTypes>());
   }
 
+#if !CAPNP_LITE
+
   {
     MallocMessageBuilder builder;
     auto root = builder.getRoot<TestAllTypes>();
@@ -1675,6 +1677,8 @@ TEST(Encoding, Embeds) {
     EXPECT_EQ(kj::str(root, '\n').size(), text.size());
   }
 
+#endif // CAPNP_LITE
+
   {
     checkTestMessage(test::EMBEDDED_STRUCT);
   }