Exclude incompatible Ruby/Solidus combo

Co-authored-by: Chris Todorov <chris@super.gd>
Co-authored-by: Adam Mueller <adam@super.gd>

Author: 3 people

.github/workflows/test.yml

@@ -39,6 +39,8 @@ jobs:
           - "mysql"
           - "sqlite"
         exclude:
+          - solidus-branch: "main"
+            ruby-version: "3.1"
           - rails-version: "7.2"
             solidus-branch: "v4.3"
           - ruby-version: "3.1"