extend/kernel: make opoo/odie/etc. print GitHub Actions notes.

We already do this for deprecations but these may make warnings
and errors from Homebrew easier to spot in GitHub Actions logs.

Library/Homebrew/dev-cmd/tests.rb

@@ -246,6 +246,9 @@ def setup_environment!
         ENV["HOMEBREW_TEST_ONLINE"] = "1" if args.online?
         ENV["HOMEBREW_SORBET_RUNTIME"] = "1"
 
+        # We don't want tests to change behaviour based on where they are run.
+        ENV.delete("GITHUB_ACTIONS")
+
         # TODO: remove this and fix tests when possible.
         ENV["HOMEBREW_NO_INSTALL_FROM_API"] = "1"
         ENV.delete("HOMEBREW_INTERNAL_JSON_V3")

Library/Homebrew/extend/kernel.rb

@@ -64,6 +64,7 @@ def oh1(title, truncate: :auto)
   def opoo(message)
     Tty.with($stderr) do |stderr|
       stderr.puts Formatter.warning(message, label: "Warning")
+      puts "::warning::#{message}" if ENV["GITHUB_ACTIONS"]
     end
   end
 
@@ -73,6 +74,7 @@ def opoo(message)
   def onoe(message)
     Tty.with($stderr) do |stderr|
       stderr.puts Formatter.error(message, label: "Error")
+      puts "::error::#{message}" if ENV["GITHUB_ACTIONS"]
     end
   end