Fix getting a single EmailDomainBlock (#20846)

app/policies/email_domain_block_policy.rb

@@ -5,6 +5,10 @@ class EmailDomainBlockPolicy < ApplicationPolicy
     role.can?(:manage_blocks)
   end
 
+  def show?
+    role.can?(:manage_blocks)
+  end
+
   def create?
     role.can?(:manage_blocks)
   end