Include the first constant name into `Ractor::IsolationError` message

If lhs of assignment is top-level constant reference, the first
constant name is omitted from error message.
This commit fixes it.

```
# shareable_constant_value: literal
::C = ["Not " + "shareable"]

# Before
# => cannot assign unshareable object to  (Ractor::IsolationError)

# After
# => cannot assign unshareable object to ::C (Ractor::IsolationError)
```

1 files changed, 26 insertions, 1 deletions

diff --git a/test/ruby/test_parse.rb b/test/ruby/test_parse.rb
index 6b8c196a84..b6d306352c 100644
--- a/test/ruby/test_parse.rb
+++ b/test/ruby/test_parse.rb
@@ -1537,12 +1537,37 @@ x = __ENCODING__
   end
 
   def test_shareable_constant_value_unshareable_literal
-    assert_raise_separately(Ractor::IsolationError, /unshareable/,
+    assert_raise_separately(Ractor::IsolationError, /unshareable object to C/,
                             "#{<<~"begin;"}\n#{<<~'end;'}")
     begin;
       # shareable_constant_value: literal
       C = ["Not " + "shareable"]
     end;
+
+    assert_raise_separately(Ractor::IsolationError, /unshareable object to B::C/,
+                            "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      # shareable_constant_value: literal
+      B = Class.new
+      B::C = ["Not " + "shareable"]
+    end;
+
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      assert_raise_with_message(Ractor::IsolationError, /unshareable object to ::C/) do
+        # shareable_constant_value: literal
+        ::C = ["Not " + "shareable"]
+      end
+    end;
+
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      assert_raise_with_message(Ractor::IsolationError, /unshareable object to ::B::C/) do
+        # shareable_constant_value: literal
+        ::B = Class.new
+        ::B::C = ["Not " + "shareable"]
+      end
+    end;
   end
 
   def test_shareable_constant_value_nonliteral