Log Message:
py-protobuf: updated to 3.9.0

Protocol Buffers v3.9.0

Python

Change implementation of Name() for enums that allow aliases in proto2 in Python
to be in line with claims in C++ implementation (to return first value).
Explicitly say what field cannot be set when the new value fails a type check.
Duplicate register in descriptor pool will raise errors
Add slots to all well_known_types classes, custom attributes are not allowed anymore.
text_format only present 8 valid digits for float fields by default