Upgrade to Postgis 3.3.4 / 3.4.0beta2 + related changes

[ImreSamu]

Context :

PostGIS 3.3.4

• https://postgis.net/2023/07/PostGIS-3.3.4-Patch-Release/
  • https://git.osgeo.org/gitea/postgis/postgis/raw/tag/3.3.4/NEWS
• pgsql-pkg-debian:"postgis updated to version 3.3.4+dfsg-1.pgdg+1"

PostGIS 3.4.0beta2

• https://postgis.net/2023/07/PostGIS-3.4.0beta2/
• https://github.com/postgis/postgis/releases/tag/3.4.0beta2
• https://github.com/postgis/postgis/blob/3.4.0beta2/NEWS

Changes:

• Postgis 3.3.3 --> 3.3.4
• 16beta2-3.3.3 --> 16beta2-3.3
  • new: postgis/postgis:16beta2-3.3 ; postgis/postgis:16beta2-3.3-alpine
  • deprecated: postgis/postgis:16beta2-3.3-3-alpine
• new 3.4.0beta2 alpine test images:
  • 15-3.4.0beta2-alpine
  • 16beta2-3.4.0beta2-alpine
• minimal refactoring: .github/workflows/main.yml ; update.sh
• updating: README.md

[ImreSamu]

Ready to review | merge