Switch from SKS to Ubuntu keyserver

See also https://github.com/docker-library/faq#openpgp--gnupg-keys-and-verification and https://github.com/tianon/pgp-happy-eyeballs

Author: tianon

10/buster/Dockerfile

@@ -75,7 +75,7 @@ RUN set -ex; \
 # uid                  PostgreSQL Debian Repository
 	key='B97B0AFCAA1A47F044F244A07FCC7D46ACCC4CF8'; \
 	export GNUPGHOME="$(mktemp -d)"; \
-	gpg --batch --keyserver ha.pool.sks-keyservers.net --recv-keys "$key"; \
+	gpg --batch --keyserver keyserver.ubuntu.com --recv-keys "$key"; \
 	gpg --batch --export "$key" > /etc/apt/trusted.gpg.d/postgres.gpg; \
 	command -v gpgconf > /dev/null && gpgconf --kill all; \
 	rm -rf "$GNUPGHOME"; \