Drop the support of Ruby 2.2

Since github flow fails to install bundler in Ruby 2.2.

The error message:
 Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby <= 2.2
  /opt/hostedtoolcache/Ruby/2.2.10/x64/bin/gem install bundler -v ~> 1.0
  ERROR:  While executing gem ... (RuntimeError)
      Marshal.load reentered at marshal_load
  Took   0.42 seconds
Error: The process '/opt/hostedtoolcache/Ruby/2.2.10/x64/bin/gem' failed with exit code 1

.github/workflows/ruby.yml

@@ -23,7 +23,7 @@ jobs:
           - ACTIVE_RECORD
           - MONGOID
         ruby:
-          - 2.2
+          - 2.3
           - 2.6
           - 2.7
           - 3.0
@@ -78,15 +78,15 @@ jobs:
           - gemfile: active_record_52.gemfile
             orm: MONGOID
           - gemfile: active_record_60.gemfile
-            ruby: 2.2
+            ruby: 2.3
           - gemfile: active_record_60.gemfile
             orm: MONGOID
           - gemfile: active_record_61.gemfile
-            ruby: 2.2
+            ruby: 2.3
           - gemfile: active_record_61.gemfile
             orm: MONGOID
           - gemfile: active_record_70.gemfile
-            ruby: 2.2
+            ruby: 2.3
           - gemfile: active_record_70.gemfile
             ruby: 2.6
           - gemfile: active_record_70.gemfile
@@ -97,8 +97,6 @@ jobs:
             ruby: 3.0
           - gemfile: mongoid_54.gemfile
             ruby: 3.1
-          - gemfile: mongoid_73.gemfile
-            ruby: 2.2
           - gemfile: mongoid_54.gemfile
             orm: ACTIVE_RECORD
           - gemfile: mongoid_64.gemfile

README.md

@@ -15,7 +15,7 @@ If you have a Rails 3 project, and want to pluck not only one column,
 feel free to use this gem and no need to worry about upgrading to Rails 4, 5, 6 in the future will break this.
 
 ## Supports
-- Ruby 2.2 ~ 2.7, 3.0 ~ 3.1
+- Ruby 2.3 ~ 2.7, 3.0 ~ 3.1
 - Rails 3.2, 4.2, 5.0, 5.1, 5.2, 6.0, 6.1, 7.0
 
 ## Installation