CI: Add Ruby 3.1 (#2782)

* CI: Add Ruby 3.1

* CI: macOS job qty to 15, remove unneeded RubyGems code

Co-authored-by: MSP-Greg <Greg.mpls@gmail.com>

.github/workflows/mri.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-20.04, ubuntu-18.04, macos-10.15, macos-11, windows-2022 ]
-        ruby: [ 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', head ]
+        ruby: [ 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, head ]
         no-ssl: ['']
         yjit: ['']
         include:
@@ -33,9 +33,11 @@ jobs:
           - { os: windows-2022 , ruby: head }
           - { os: macos-10.15  , ruby: 2.6  }
           - { os: macos-10.15  , ruby: 2.7  }
-          - { os: macos-10.15  , ruby: '3.0' }
+          - { os: macos-10.15  , ruby: '3.0'}
+          - { os: macos-10.15  , ruby: 3.1  }
           - { os: macos-11     , ruby: 2.2  }
           - { os: macos-11     , ruby: 2.3  }
+          - { os: macos-11     , ruby: 2.4  }
 
     steps:
       - name: repo checkout
@@ -59,13 +61,6 @@ jobs:
         continue-on-error: true
         timeout-minutes: 5
 
-      # Fix RubyGems warnings about required_ruby_version bug with Bundler
-      - name: update rubygems for Ruby 2.3 - 2.5
-        if: matrix.ruby >= '2.3' && matrix.ruby < '2.6'
-        run: gem update --system 3.2.3 --no-document
-        continue-on-error: true
-        timeout-minutes: 5
-
       - name: Compile Puma without SSL support
         if: matrix.no-ssl == ' no SSL'
         shell: bash