DEV: Correctly tag heredocs (#16061)

This allows text editors to use correct syntax coloring for the heredoc sections.

Heredoc tag names we use:

languages: SQL, JS, RUBY, LUA, HTML, CSS, SCSS, SH, HBS, XML, YAML/YML, MF, ICS
other: MD, TEXT/TXT, RAW, EMAIL

plugins/poll/spec/lib/new_post_manager_spec.rb

@@ -39,12 +39,12 @@ describe NewPostManager do
     end
 
     it 're-validates the poll when the approve_post event is triggered' do
-      invalid_raw_poll = <<~RAW
+      invalid_raw_poll = <<~MD
         [poll type=multiple min=0]
         * 1
         * 2
         [/poll]
-      RAW
+      MD
 
       result = NewPostManager.new(user, params).perform