Require Ruby 2.6.8

Library/Homebrew/brew.sh

@@ -458,9 +458,7 @@ then
 
   # Set a variable when the macOS system Ruby is new enough to avoid spawning
   # a Ruby process unnecessarily.
-  # On Catalina the system Ruby is technically new enough but don't allow it:
-  # https://github.com/Homebrew/brew/issues/9410
-  if [[ "${HOMEBREW_MACOS_VERSION_NUMERIC}" -lt "101600" ]]
+  if [[ "${HOMEBREW_MACOS_VERSION_NUMERIC}" -lt "120000" ]]
   then
     unset HOMEBREW_MACOS_SYSTEM_RUBY_NEW_ENOUGH
   else

Library/Homebrew/extend/os/mac/diagnostic.rb

@@ -201,19 +201,12 @@ module Homebrew
       end
 
       def check_ruby_version
-        # TODO: require 2.6.8 for everyone once enough have updated to Monterey
-        required_version = if MacOS.version >= :monterey ||
-                              ENV["HOMEBREW_RUBY_PATH"].to_s.include?("/vendor/portable-ruby/")
-          "2.6.8"
-        else
-          HOMEBREW_REQUIRED_RUBY_VERSION
-        end
-        return if RUBY_VERSION == required_version
+        return if RUBY_VERSION == HOMEBREW_REQUIRED_RUBY_VERSION
         return if Homebrew::EnvConfig.developer? && OS::Mac.version.prerelease?
 
         <<~EOS
           Ruby version #{RUBY_VERSION} is unsupported on macOS #{MacOS.version}. Homebrew
-          is developed and tested on Ruby #{required_version}, and may not work correctly
+          is developed and tested on Ruby #{HOMEBREW_REQUIRED_RUBY_VERSION}, and may not work correctly
           on other Rubies. Patches are accepted as long as they don't cause breakage
           on supported Rubies.
         EOS

Library/Homebrew/utils/ruby.sh

@@ -1,4 +1,4 @@
-export HOMEBREW_REQUIRED_RUBY_VERSION=2.6.3
+export HOMEBREW_REQUIRED_RUBY_VERSION=2.6.8
 
 # HOMEBREW_LIBRARY is from the user environment
 # shellcheck disable=SC2154