tests/cpydiff: Add case for difference in behaviour of bytes.format().

tests/cpydiff/types_bytes_format.py

@@ -0,0 +1,7 @@
+"""
+categories: Types,bytes
+description: bytes objects support .format() method
+cause: MicroPython strives to be a more regular implementation, so if both `str` and `bytes` support ``__mod__()`` (the % operator), it makes sense to support ``format()`` for both too. Support for ``__mod__`` can also be compiled out, which leaves only ``format()`` for bytes formatting.
+workaround: If you are interested in CPython compatibility, don't use ``.format()`` on bytes objects.
+"""
+print(b'{}'.format(1))