Remove Ruby v2.6 (eol)

Author: esotericpig

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
       matrix:
         os: [ 'ubuntu-latest', 'macos-latest' ]
         # - https://www.ruby-lang.org/en/downloads/branches
-        ruby-version: [ '2.6', '3.1', '3.2', '3.3', 'ruby-head' ]
+        ruby-version: [ '3.1', '3.2', '3.3', 'ruby-head' ]
 
     runs-on: ${{ matrix.os }}