Update docker image to bullseye

This updates us to bullseye on our docker image.

Change-Id: Id7d4bcee76de84c55f15d2f9ee6970bc5f29bd0a

.zuul.yaml

@@ -19,6 +19,9 @@
     parent: opendev-build-docker-image
     description: Build OpenDev Docker images for storyboard webclient
     provides: gerritbot-container-image
+    requires:
+      - python-builder-3.8-bullseye-container-image
+      - python-base-3.8-bullseye-container-image
     required-projects: &gerritbot_opendev_required_projects
       - opendev/gerritlib
     vars: &gerritbot_opendev_image_vars
@@ -35,6 +38,9 @@
     parent: opendev-upload-docker-image
     description: Build OpenDev gerritbot Docker images and upload to Docker Hub.
     provides: gerritbot-container-image
+    requires:
+      - python-builder-3.8-bullseye-container-image
+      - python-base-3.8-bullseye-container-image
     required-projects: *gerritbot_opendev_required_projects
     vars: *gerritbot_opendev_image_vars
     secrets:

Dockerfile

@@ -13,12 +13,12 @@
 # You should have received a copy of the GNU General Public License
 # along with this software.  If not, see <http://www.gnu.org/licenses/>.
 
-FROM opendevorg/python-builder:3.8 as builder
+FROM opendevorg/python-builder:3.8-bullseye as builder
 
 COPY . /tmp/src
 RUN assemble
 
-FROM opendevorg/python-base:3.8 as gerritbot
+FROM opendevorg/python-base:3.8-bullseye as gerritbot
 
 COPY --from=builder /output/ /output
 RUN /output/install-from-bindep