test on all rubies from 2.6 to 3.4

Author: mackuba

.github/workflows/main.yml

@@ -14,10 +14,13 @@ jobs:
     strategy:
       matrix:
         ruby:
+          - '2.6'
           - '2.7'
           - '3.0'
           - '3.1'
           - '3.2'
+          - '3.3'
+          - '3.4'
 
     steps:
     - uses: actions/checkout@v3