Replace keys.gnupg.net.

I didn't follow what happened but it's seems like it's decomissioned.

Dockerfile

@@ -19,7 +19,7 @@ RUN apt-get update && \
     gpg --no-default-keyring --import --batch --keyring /usr/share/keyrings/hashicorp.gpg && \
     curl https://dl.cloudsmith.io/public/cloudposse/packages/gpg.7333C6FDEFA717CC.key | \
     gpg --no-default-keyring --import --batch --keyring /usr/share/keyrings/cloudposse.gpg && \
-    gpg --no-default-keyring --keyring /usr/share/keyrings/percona.gpg --keyserver keys.gnupg.net --recv-keys 9334A25F8507EFA5 && \
+    gpg --no-default-keyring --keyring /usr/share/keyrings/percona.gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 9334A25F8507EFA5 && \
     gpg --no-default-keyring --keyring /usr/share/keyrings/clickhouse.gpg --keyserver hkp://keyserver.ubuntu.com:80  --recv-keys 8919F6BD2B48D754 && \
     rm -rf /tmp/* /var/tmp/* /var/lib/apt/lists/* /var/cache/apt/archives/*
 COPY --chown=root:root sources.d/* /etc/apt/sources.list.d/