Update release platforms. (#55)

Drop Ubuntu Xenial.
Add Ubuntu Jammy.
Add Debian Bullseye.

Author: nuclearsandwich

publish-python.yaml

@@ -8,8 +8,9 @@ artifacts:
         config:
           repository: dirk-thomas/colcon
           distributions:
-            - ubuntu:xenial
             - ubuntu:bionic
             - ubuntu:focal
+            - ubuntu:jammy
             - debian:stretch
             - debian:buster
+            - debian:bullseye