gh-131357: Add a set of asserts to test.test_capi.test_bytearray (#131554)

add a set of asserts to test.test_capi.test_bytearray

1. Assert empty bytearray object for PyByteArray_Check.
2. Assert empty bytearray object for PyByteArray_CheckExact.
3. Assert 0-size bytearray object for PyByteArray_Size.
4. Assert empty bytearray object for PyByteArray_AsString.
5. Assert concatenation of the bytearray object with itself for PyByteArray_Concat.