chore: new owl bot post processor docker image (#53)

gcr.io/repo-automation-bots/owlbot-python:latest@sha256:3c3a445b3ddc99ccd5d31edc4b4519729635d20693900db32c4f587ed51f7479

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/repo-automation-bots/owlbot-python:latest
-  digest: sha256:4c981a6b6f2b8914a448d7b3a01688365be03e3ed26dfee399a6aa77fb112eaa
+  digest: sha256:3c3a445b3ddc99ccd5d31edc4b4519729635d20693900db32c4f587ed51f7479

noxfile.py

@@ -179,7 +179,7 @@ def docs(session):
     """Build the docs for this library."""
 
     session.install("-e", ".")
-    session.install("sphinx", "alabaster", "recommonmark")
+    session.install("sphinx==4.0.1", "alabaster", "recommonmark")
 
     shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
     session.run(
@@ -201,7 +201,9 @@ def docfx(session):
     """Build the docfx yaml files for this library."""
 
     session.install("-e", ".")
-    session.install("sphinx", "alabaster", "recommonmark", "gcp-sphinx-docfx-yaml")
+    session.install(
+        "sphinx==4.0.1", "alabaster", "recommonmark", "gcp-sphinx-docfx-yaml"
+    )
 
     shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
     session.run(