Update github actions run

This gem doesn't yet support Solidus 4+, so we can't run it against
Rails > 7.0.

Author: kjriga

.github/workflows/test.yml

@@ -19,8 +19,7 @@ jobs:
       fail-fast: true
       matrix:
         rails-version:
-          - "7.1"
-          - "7.2"
+          - "7.0"
         ruby-version:
           - "3.1"
           - "3.2"