remove ruby 2.5 tests

Author: SpringMT

.github/workflows/ruby.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.5', '2.6', '2.7', '3.0', '3.1']
+        ruby-version: ['2.6', '2.7', '3.0', '3.1']
 
     steps:
     - uses: actions/checkout@v2