Dockerfile: Get GPG key from IPv4 servers only

Fix #3610
3 jobs for feature-s/3610-gpg-keyserver in 7 minutes and 8 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test Tools
passed #197590
test_tools

00:00:06

 
  Test Unit
passed #197591
web
test_server_unit

00:00:18

 
  Test Functional
passed #197592
docker x86_64
test_server_functional

00:06:42