pgdg-keyring (or apt-key) failure on fresh 9.6 install

Hi folks,
I'm trying to install Postgresql 9.6 on a test machine in Google Cloud
Platform
After a fresh install with Debian 9 (just after the instance has been
created) I follow steps from here

https://wiki.postgresql.org/wiki/Apt

(instead of pg 10 I install pg 9.6)

During the installation process i encounter the following strange
warnings that, even if that's a test machine, make me think twice before
going ahead.

[...]
Processing triggers for man-db (2.7.6.1-2) ...
Setting up pgdg-keyring (2017.3) ...
Removing apt.postgresql.org key from trusted.gpg: Warning: The postinst
maintainerscript of the package pgdg-keyring
Warning: seems to use apt-key (provided by apt) without depending on
gnupg or gnupg2.
Warning: This will BREAK in the future and should be fixed by the
package maintainer(s).
Note: Check first if apt-key functionality is needed at all - it
probably isn't!
OK
Setting up xml-core (0.17) ...
[...]

I have to say that installation is successfully and database server goes
up and apparently with no problems at all.

Here's versions:

postgres=# select version();

version
------------------------------------------------------------------------------------------------------------------------------------

PostgreSQL 9.6.9 on x86_64-pc-linux-gnu (Debian 9.6.9-2.pgdg90+1),
compiled by gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516, 64-bit(1 row)

Anyone stumped on it? Googling around I see a post saying that's about a
dirmngr package missing.... tried but no avail.

Do I need to worry?

Thanks

Moreno.-