fix ruby test matrix

Author: haru

.github/workflows/build.yml

@@ -10,8 +10,13 @@ jobs:
     strategy:
       matrix:
         db: [sqlite3, mysql, postgres]
-        ruby_version: ["3.1", "3.2", "3.3"]
+        ruby_version: ["3.1", "3.2", "3.3", "3.4"]
         redmine_version: [6.0-stable, master]
+        exclude:
+          - ruby_version: "3.4"
+            redmine_version: 6.0-stable
+          - ruby_version: "3.1"
+            redmine_version: master
     services:
       mysql:
         image: mysql:5.7