Stop testing Ruby 2.2 in CI as it no longer works with ubuntu-latest

Author: jeremyevans

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-20.04 ]
-        ruby: [ 2.0.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, jruby-9.3, jruby-9.4 ]
+        ruby: [ 2.0.0, 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, jruby-9.3, jruby-9.4 ]
         gemfile: [ Gemfile, Gemfile.rack-1.x ]
         exclude:
           - ruby: 2.0.0