ARROW-7791: [C++][Parquet] Fix building error "cannot bind lvalue"

https://issues.apache.org/jira/browse/ARROW-7791

Closes #6381 from plusplusjiajia/arrow-read-write-test and squashes the following commits:

d08f99c <Li, Jiajia> Fix building error cannot bind lvalue

Authored-by: Li, Jiajia <jiajia.li@intel.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

cpp/src/parquet/arrow/arrow_reader_writer_test.cc

@@ -2897,7 +2897,7 @@ class TestArrowReadDictionary : public ::testing::TestWithParam<double> {
     RETURN_NOT_OK(builder.Open(std::make_shared<BufferReader>(buffer_)));
     RETURN_NOT_OK(builder.properties(properties_)->Build(&reader));
 
-    return reader;
+    return std::move(reader);
   }
 };