chore: allow releases on previous major versions (#295)

* chore: allow releases on previous major versions

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: parthea

.github/release-please.yml

@@ -1,2 +1,11 @@
 releaseType: python
 handleGHRelease: true
+# NOTE: this section is generated by synthtool.languages.python
+# See https://github.com/googleapis/synthtool/blob/master/synthtool/languages/python.py
+branches:
+- branch: v1
+  handleGHRelease: true
+  releaseType: python
+- branch: v0
+  handleGHRelease: true
+  releaseType: python

owlbot.py

@@ -107,6 +107,8 @@ def get_staging_dirs(
 
 python.py_samples(skip_readmes=True)
 
+python.configure_previous_major_version_branches()
+
 # Preserve system tests w/ GOOGLE_DISABLE_GRPC set (#133, PR #136)
 assert 1 == s.replace(
     "noxfile.py",