chore(deps): update dependency protobuf to v3.18.1 (#1008)

Co-authored-by: Dov Shlachter <[email protected]>

Author: renovate-bot

packages/gapic-generator/requirements.txt

@@ -3,7 +3,7 @@ google-api-core==2.1.0
 googleapis-common-protos==1.53.0
 jinja2==3.0.1
 MarkupSafe==2.0.1
-protobuf==3.18.0
+protobuf==3.18.1
 pypandoc==1.6.4
 PyYAML==5.4.1
 dataclasses==0.6  # TODO(busunkim) remove when 3.6 support is dropped