deprecate ruby 2.7, test ruby >3.0 only

Author: spiderpug

.github/workflows/ci.yml

@@ -8,15 +8,16 @@ on:
 
 jobs:
   rspec:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
         ruby:
+          - '3.4'
+          - '3.3'
           - '3.2'
           - '3.1'
           - '3.0'
-          - '2.7'
     steps:
       - name: Checkout
         uses: actions/checkout@v2