chore(cloudbuild): fix broken synth file (#10077)

Author: busunkim96

cloudbuild/synth.py

@@ -39,9 +39,9 @@
  'nox*.py',
  'setup.py',
  'setup.cfg',
- 'README.rst'
- '**/*.proto'
- 'google/cloud/devtools/__init__.py' # declare this as a namespace package
+ 'README.rst',
+ '**/*.proto',
+ 'google/cloud/devtools/__init__.py', # declare this as a namespace package
  ],
 )