pull: only add gpg to path if enabled in git

Library/Homebrew/dev-cmd/pull.rb

@@ -103,6 +103,7 @@ module Homebrew
     end
 
     # Depending on user configuration, git may try to invoke gpg.
+    if Utils.popen_read("git config --get --bool commit.gpgsign").chomp == "true"
       begin
         gnupg = Formula["gnupg"]
       rescue FormulaUnavailableError # rubocop:disable Lint/HandleExceptions
@@ -113,6 +114,7 @@ module Homebrew
           ENV["PATH"] = path
         end
       end
+    end
 
     do_bump = @args.bump? && !@args.clean?