Update the zuul client docker image to bullseye

Bullseye has been out for a bit now and buster has a shelf life. Update
to bullseye to keep up with the debian releases.

Change-Id: Ib4c0fea0da33352009ab15c44891824466a78954

.zuul.yaml

@@ -21,8 +21,8 @@
     allowed-projects: zuul/zuul-client
     timeout: 2700
     requires:
-      - python-builder-3.8-container-image
-      - python-base-3.8-container-image
+      - python-builder-3.8-bullseye-container-image
+      - python-base-3.8-bullseye-container-image
     provides:
       - zuul-client-container-image
     vars: &zuulclient_image_vars
@@ -38,8 +38,8 @@
     description: Build the CLI Docker image and upload to Docker Hub.
     timeout: 3600
     requires:
-      - python-builder-3.8-container-image
-      - python-base-3.8-container-image
+      - python-builder-3.8-bullseye-container-image
+      - python-base-3.8-bullseye-container-image
     provides: zuul-client-container-image
     vars: *zuulclient_image_vars
     secrets:

Dockerfile

@@ -13,12 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM docker.io/opendevorg/python-builder:3.8 as builder
+FROM docker.io/opendevorg/python-builder:3.8-bullseye as builder
 
 COPY . /tmp/src
 RUN assemble
 
-FROM docker.io/opendevorg/python-base:3.8
+FROM docker.io/opendevorg/python-base:3.8-bullseye
 
 COPY --from=builder /output/ /output
 RUN /output/install-from-bindep