Remove Ruby 2.6 from testing, use Ruby 2.7 instead.

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Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: dblock

.github/workflows/rspec.yml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       matrix:
         entry:
-          - { ruby: '2.6', mongodb: '4.4', gemfile: 'mongoid_4', bundler: '1.17.3' }
+          - { ruby: '2.7', mongodb: '4.4', gemfile: 'mongoid_4', bundler: '1.17.3' }
           - { ruby: '2.7', mongodb: '4.4', gemfile: 'mongoid_5', bundler: '1.17.3' }
           - { ruby: '2.7', mongodb: '4.4', gemfile: 'mongoid_6', bundler: '2.4.19' }
           - { ruby: '2.7', mongodb: '4.4', gemfile: 'mongoid_7', bundler: '2.4.19' }