Add Ruby 3.1 to the CI matrix

Author: petergoldstein

.github/workflows/main.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ["2.5", "2.6", "2.7", "3.0"]
+        ruby: ["2.5", "2.6", "2.7", "3.0", "3.1"]
     name: Ruby ${{ matrix.ruby }}
 
     steps:

Gemfile

@@ -2,3 +2,9 @@
 
 source 'https://rubygems.org'
 gemspec
+
+if Gem::Version.new(RUBY_VERSION.dup) >= Gem::Version.new('3.1')
+  gem 'net-imap', require: false
+  gem 'net-pop', require: false
+  gem 'net-smtp', require: false
+end