postgis update wants to install postgresql-13

Hi there,

i hope i'm right here... i just wanted to install some debian updates
(buster) and saw that there are postgres/postgis updates as well.
Currently installed:

postgis 3.0.2+dfsg-2.pgdg100+1
postgis-doc 3.0.2+dfsg-2.pgdg100+1
postgresql-12 12.4-1.pgdg100+1
postgresql-12-postgis-2.5 2.5.5+dfsg-1.pgdg100+1
postgresql-12-postgis-2.5-scripts 2.5.5+dfsg-1.pgdg100+1
postgresql-12-postgis-3 3.0.2+dfsg-2.pgdg100+1
postgresql-12-postgis-3-scripts 3.0.2+dfsg-2.pgdg100+1

I use postgis extension in v2.5. The postgis package is needed for
shp2pgsql etc. Upgradeable packages are:

postgis-doc/buster-pgdg 3.0.2+dfsg-4.pgdg100+1 all [upgradable from:
3.0.2+dfsg-2.pgdg100+1]
postgis/buster-pgdg 3.0.2+dfsg-4.pgdg100+1 amd64 [upgradable from:
3.0.2+dfsg-2.pgdg100+1]
postgresql-12-postgis-3-scripts/buster-pgdg 3.0.2+dfsg-4.pgdg100+1 all
[upgradable from: 3.0.2+dfsg-2.pgdg100+1]
postgresql-12-postgis-3/buster-pgdg 3.0.2+dfsg-4.pgdg100+1 amd64
[upgradable from: 3.0.2+dfsg-2.pgdg100+1]
postgresql-client-common/buster-pgdg 220.pgdg100+1 all [upgradable
from: 217.pgdg100+1]
postgresql-common/buster-pgdg 220.pgdg100+1 all [upgradable from: 217.pgdg100+1]

But there are some unexpected packages to be installed:

The following NEW packages will be installed:
postgresql-13 postgresql-13-postgis-3 postgresql-13-postgis-3-scripts
postgresql-client-13

If i get it right for the minor postgis update now postgresql-13 will
be installed. Is there any reason for this?

Best regards,
Hubert