chore: store artifacts in placer (#1678)

Source-Link: googleapis/synthtool@cb96037
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:2d816f26f728ac8b24248741e7d4c461c09764ef9f7be3684d557c9632e46dbd

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

Author: gcf-owl-bot[bot]

packages/gapic-generator/.github/.OwlBot.lock.yaml

@@ -13,5 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:240b5bcc2bafd450912d2da2be15e62bc6de2cf839823ae4bf94d4f392b451dc
-# created: 2023-06-03T21:25:37.968717478Z
+  digest: sha256:2d816f26f728ac8b24248741e7d4c461c09764ef9f7be3684d557c9632e46dbd
+# created: 2023-06-28T17:03:33.371210701Z

packages/gapic-generator/.kokoro/release/common.cfg

@@ -38,3 +38,12 @@ 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 {
+  define_artifacts {
+    regex: "github/gapic-generator-python/**/*.tar.gz"
+    strip_prefix: "github/gapic-generator-python"
+  }
+}