chore: update post processor image (#13197)

This PR updates the post processor image to the latest one which is
`gcr.io/cloud-devrel-public-resources/owlbot-python-mono-repo@sha256:db9568404b062e3bcf060fb7db09ca9aa51275d187b0f4ccd5f0071e82e4521a`.

The latest image includes the following PR:
googleapis/synthtool#2023

Run the following commands to obtain the latest sha256
```
docker pull gcr.io/cloud-devrel-public-resources/owlbot-python-mono-repo:latest
```

```
docker inspect --format='{{.RepoDigests}}' gcr.io/cloud-devrel-public-resources/owlbot-python-mono-repo:latest
[gcr.io/cloud-devrel-public-resources/owlbot-python-mono-repo@sha256:db9568404b062e3bcf060fb7db09ca9aa51275d187b0f4ccd5f0071e82e4521a]
```

.github/.OwlBot.lock.yaml

@@ -13,4 +13,4 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python-mono-repo:latest
-  digest: sha256:93fe03a099be9aa70157b95f5600473602d53b34983488ccdcd37cecb6a9ba3e
+  digest: sha256:db9568404b062e3bcf060fb7db09ca9aa51275d187b0f4ccd5f0071e82e4521a

.kokoro/release/common.cfg

@@ -33,12 +33,6 @@ before_action {
   }
 }
 
-# Tokens needed to report release status back to GitHub
-env_vars: {
-  key: "SECRET_MANAGER_KEYS"
-  value: "releasetool-publish-reporter-app,releasetool-publish-reporter-googleapis-installation,releasetool-publish-reporter-pem"
-}
-
 # Store the packages we uploaded to PyPI.  That way, we have a record of exactly
 # what we published, which we can use to generate SBOMs and attestations.
 action {