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

app/controllers/session_controller.rb

@@ -247,7 +247,7 @@ class SessionController < ApplicationController
     rescue ActiveRecord::RecordInvalid => e
 
       if SiteSetting.verbose_discourse_connect_logging
-        Rails.logger.warn(<<~EOF)
+        Rails.logger.warn(<<~TEXT)
         Verbose SSO log: Record was invalid: #{e.record.class.name} #{e.record.id}
         #{e.record.errors.to_h}
 
@@ -256,7 +256,7 @@ class SessionController < ApplicationController
 
         SSO Diagnostics:
         #{sso.diagnostics}
-        EOF
+        TEXT
       end
 
       text = nil