Adjust the regex for lsn spec

lsns are hexadecimal locators which include A-F
https://www.postgresql.org/docs/current/datatype-pg-lsn.html

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/324682

ee/spec/lib/gitlab/database/load_balancing/load_balancer_spec.rb

@@ -244,7 +244,7 @@ RSpec.describe Gitlab::Database::LoadBalancing::LoadBalancer, :request_store do
 
   describe '#primary_write_location' do
     it 'returns a String in the right format' do
-      expect(lb.primary_write_location).to match(/[A-E0-9]{1,8}\/[A-E0-9]{1,8}/)
+      expect(lb.primary_write_location).to match(/[A-F0-9]{1,8}\/[A-F0-9]{1,8}/)
     end
 
     it 'raises an error if the write location could not be retrieved' do