Add Ruby 3.1 to the supported Ruby versions (#36205).

git-svn-id: http://svn.redmine.org/redmine/trunk@21329 e93f8b46-1217-0410-a6f0-8f06a7374b81

Gemfile

@@ -1,6 +1,6 @@
 source 'https://rubygems.org'
 
-ruby '>= 2.5.0', '< 3.1.0'
+ruby '>= 2.5.0', '< 3.2.0'
 gem 'bundler', '>= 1.12.0'
 
 gem 'rails', '6.1.4.4'

doc/INSTALL

@@ -7,7 +7,7 @@ http://www.redmine.org/
 
 == Requirements
 
-* Ruby 2.5, 2.6, 2.7, 3.0
+* Ruby 2.5, 2.6, 2.7, 3.0, 3.1
 * Bundler >= 1.12.0
 
 * A database: