ci: Stop trying to pull out the default extra-args.

This was preventing the 20.04 install from actually happening, as
GitHub was folding the two into one configuration.

.github/workflows/production-suite.yml

@@ -126,17 +126,18 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        extra-args: [""]
         include:
           # Docker images are built from 'tools/ci/Dockerfile'; the comments at
           # the top explain how to build and upload these images.
           - docker_image: zulip/ci:focal
             name: Ubuntu 20.04 production install
             os: focal
+            extra-args: ""
 
           - docker_image: zulip/ci:jammy
             name: Ubuntu 22.04 production install
             os: jammy
+            extra-args: ""
 
           - docker_image: zulip/ci:bullseye
             name: Debian 11 production install with custom db name and user