⬇️ Continue testing 0.3.x branch against ruby 2.6

Author: nevans

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     uses: ruby/actions/.github/workflows/ruby_versions.yml@master
     with:
       engine: cruby
-      min_version: 2.7
+      min_version: 2.6
 
   build:
     needs: ruby-versions