How to create stable images (Version '<version>' for 'postgresql-<version>-postgis-<version>' was not found)

[petetnt]

Re-opening this issue because it's similar to the following issue https://github.com/postgis/docker-postgis/issues/346 but I'd like to find a more long term solution than just updating the version in the variable.

I am not really familiar how the apt release process works at all, but basically currently every(ish?) time a new version is released, the version we are using is removed (eg. see https://ftp.debian.org/debian/pool/main/p/postgis/), which means that the version variable POSTGIS_VERSION needs to be updated.

For example, the version pointed at now, 3.4.3+dfsg-2.pgdg110+1 results in the following error:

0 2.931 Provides:
#0 2.931 3.5.0+dfsg-1.pgdg120+1 - postgresql-15-postgis (= )
#0 2.931 3.3.2+dfsg-1+b1 - postgresql-15-postgis (= )
#0 2.931 Reverse Provides:
#0 2.948 Reading package lists...
#0 3.284 Building dependency tree...
#0 3.369 Reading state information...
#0 3.374 Package postgresql-15-postgis-3 is not available, but is referred to by another package.
#0 3.374 This may mean that the package is missing, has been obsoleted, or
#0 3.374 is only available from another source
#0 3.374
#0 3.381 E: Version '3.4.3+dfsg-2.pgdg110+1' for 'postgresql-15-postgis-3' was not found

I am looking for a way to make this somewhat stable, eg. I am okay with just 3.4.3 as long as it's available until I update it.

As far as I understand, @sebastic manages the releases on the Debian side if I understand https://tracker.debian.org/pkg/postgis correctly, so maybe they could throw a pointer or two what should be the proposed way forward.