golang_str: tests: Fix test_strings_refcount wrt upcoming str=bstr and unicode=ustr

When gpython will start patching builtin str and unicode types with bstr
and ustr it might be the case that b('abc') return the same 'abc' object
and so the logic in this test will become broken.

-> Avoid that by keeping the original data in bytearray which for sure
   won't overlap with bytes/str nor unicode irregardless whether those
   builtin types are patched or not.

golang/golang_str_test.py

@@ -288,20 +288,26 @@ def test_strings_basic():
 
 # verify that bstr/ustr are created with correct refcount.
 def test_strings_refcount():
+    # buffer with string data - not bytes nor unicode so that when builtin
+    # string types are patched there is no case where bytes is created from the
+    # same bytes, or unicode is created from the same unicode - only increasing
+    # refcount of original object.
+    data = bytearray([ord('a'), ord('b'), ord('c'), ord('4')])
+
     # first verify our logic on std type
-    obj = xbytes(u'abc');   assert type(obj) is bytes
+    obj = bytes(data);      assert type(obj) is bytes
     gc.collect();   assert sys.getrefcount(obj) == 1+1   # +1 due to obj passed to getrefcount call
 
     # bstr
-    obj = b('abc');         assert type(obj) is bstr
+    obj = b(data);          assert type(obj) is bstr
     gc.collect();           assert sys.getrefcount(obj) == 1+1
-    obj = bstr('abc');      assert type(obj) is bstr
+    obj = bstr(data);       assert type(obj) is bstr
     gc.collect();           assert sys.getrefcount(obj) == 1+1
 
     # ustr
-    obj = u('abc');         assert type(obj) is ustr
+    obj = u(data);          assert type(obj) is ustr
     gc.collect();           assert sys.getrefcount(obj) == 1+1
-    obj = ustr('abc');      assert type(obj) is ustr
+    obj = ustr(data);       assert type(obj) is ustr
     gc.collect();           assert sys.getrefcount(obj) == 1+1