diagnostic: ignore case in origin comparison

On circle-ci we do:
git remote set-url origin $CIRCLE_REPOSITORY_URL

which is defined as: https://github.com/linuxbrew/homebrew-core

This is being compared to:
https://github.com/Linuxbrew/homebrew-core

Library/Homebrew/diagnostic.rb

@@ -583,7 +583,7 @@ module Homebrew
             properly. You can solve this by adding the Homebrew remote:
               git -C "#{coretap_path}" remote add origin #{Formatter.url(CoreTap.instance.default_remote)}
           EOS
-        elsif origin !~ %r{#{CoreTap.instance.full_name}(\.git|/)?$}
+        elsif origin !~ %r{#{CoreTap.instance.full_name}(\.git|/)?$}i
           <<~EOS
             Suspicious #{CoreTap.instance} git origin remote found.