Disable test for ruby-dev & grape 1.8.0

Author: numbata

.github/workflows/ci.yml

@@ -30,7 +30,6 @@ jobs:
           - { ruby: '3.2', grape: '1.8.0' }
           - { ruby: '3.3', grape: '1.8.0' }
           - { ruby: '3.4', grape: '1.8.0' }
-          - { ruby: 'head', grape: '1.8.0' }
           - { ruby: '3.1', grape: '2.0.0' }
           - { ruby: '3.2', grape: '2.0.0' }
           - { ruby: '3.3', grape: '2.0.0' }