chore(python): include py.typed files in release

A py.typed file must be included in the released package for it to be considered typed by type checkers. https://www.python.org/dev/peps/pep-0561/#packaging-type-information. See googleapis/python-secret-manager#79

Source-Author: Bu Sun Kim <[email protected]>
Source-Date: Fri Feb 5 17:32:06 2021 -0700
Source-Repo: googleapis/synthtool
Source-Sha: 33366574ffb9e11737b3547eb6f020ecae0536e8
Source-Link: googleapis/synthtool@3336657

Author: yoshi-automation

MANIFEST.in

@@ -16,10 +16,10 @@
 
 # Generated by synthtool. DO NOT EDIT!
 include README.rst LICENSE
-recursive-include google *.json *.proto
+recursive-include google *.json *.proto py.typed
 recursive-include tests *
 global-exclude *.py[co]
 global-exclude __pycache__
 
 # Exclude scripts for samples readmegen
-prune scripts/readme-gen
+prune scripts/readme-gen

synth.metadata

@@ -11,7 +11,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "d1bb9173100f62c0cfc8f3138b62241e7f47ca6a"
+        "sha": "33366574ffb9e11737b3547eb6f020ecae0536e8"
       }
     }
   ],