Take the minor version of Ruby into account

The numeric version `3.0` is treated as `3`. As result, the latest Ruby 3.x version s used for testing instead of Ruby 3.0.
Using the text notation `'3.0'` makes Github Action to use the proper version for testing (Ruby 3.0)

.github/workflows/test.yml

@@ -23,11 +23,11 @@ jobs:
       fail-fast: false
       matrix:
         ruby-version: 
-          - 2.7
-          - 3.0
-          - 3.1
-          - 3.2
-          - 3.3
+          - '2.7'
+          - '3.0'
+          - '3.1'
+          - '3.2'
+          - '3.3'
 
     steps:
     - uses: actions/checkout@v3