upgrade: apine postgis 3.5.3 -alpine; add: 3.6.0alpha1

[ImreSamu]

changes:

• upgrade: 1*-3.5-alpine to 3.5.3
• new test : 17-3.6.0alpha1-alpine
• alpine,master : add --verbose to check RUNTESTFLAGS="--extension --verbose"

other:

• improve ./update.sh
• bump 'DOCKER_APT_PKG_VER:' ( docker ci )
  fixing : https://github.com/postgis/docker-postgis/actions/runs/15105096310

comment:

• Debian 3.5 postgis is still on 3.5.2 :
  • https://www.postgresql.org/message-id/E1uH3Gq-0047R5-Du%40atalia.postgresql.org

[phillipross]

lgtm, thanks!