4.0.6

Special thanks to the contributors that made this release happen: @cjp256 and @sergiusens

Bug Fixes

• extensions: add gcc to GNOME 3.28 extension part @sergiusens (#3178)
• repo: decouple fetch and unpack stage-packages @sergiusens (#3170)
• repo: consider virtual pkgs for cache invalidation @sergiusens (#3177)
• cli: restore --target-arch with warning for LXD and Multipass @cjp256 (#3175)
• package-repositories: allow empty component list @cjp256 (#3169)

Maintenance

• unit tests: move to pytest @sergiusens (#3167)