create dedicated group for spring boot

Author: yeikel

.github/dependabot.yml

@@ -14,7 +14,11 @@ updates:
     - "type/dependencies"
     - "scope/backend"
   groups:
-    gradle-dependencies:
+    spring-boot-dependencies:
+      patterns:
+        - "org.springframework.boot:*"
+        - "io.spring.dependency-management"
+    other-dependencies:
       patterns:
         - "*"
       update-types: