chore: allow releases on previous major versions (#1134)

* 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 +1,8 @@
 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: v0
+  handleGHRelease: true
+  releaseType: python

owlbot.py

@@ -92,7 +92,6 @@
     system_test_extras=["testing"],
     microgenerator=True,
 )
-python.py_samples(skip_readmes=True)
 s.move(
     templated_files,
     excludes=[
@@ -104,6 +103,10 @@
     ],
 )  # the microgenerator has a good coveragerc file
 
+python.py_samples(skip_readmes=True)
+
+python.configure_previous_major_version_branches()
+
 # Update samples config to use `ucaip-sample-tests` project
 s.replace(
     ".kokoro/samples/python3.*/common.cfg",