sudo: sudo_as_root should apply on top of HOMEBREW_SUDO_THROUGH_SUDO_USER

System commands run with sudo_as_root must be run as  regardless of who is running sudo.

Library/Homebrew/system_command.rb

@@ -190,7 +190,8 @@ class SystemCommand
                      *askpass_flags,
                      "-E", *env_args,
                      "--", "/usr/bin/sudo"]
-    elsif sudo_as_root?
+    end
+    if sudo_as_root?
       user_flags += ["-u", "root"]
     end
     ["/usr/bin/sudo", *user_flags, *askpass_flags, "-E", *env_args, "--"]