chore: update Spring Boot/Framework testing matrix (#64)

Author: rammrain

.github/spring-versions.json

@@ -1,40 +1,5 @@
 {
   "matrix": [
-    {
-      "boot": "3.0.13",
-      "framework": "6.0.14",
-      "java": "17"
-    },
-    {
-      "boot": "3.1.11",
-      "framework": "6.0.20",
-      "java": "17"
-    },
-    {
-      "boot": "3.1.12",
-      "framework": "6.0.21",
-      "java": "21"
-    },
-    {
-      "boot": "3.2.12",
-      "framework": "6.1.15",
-      "java": "17"
-    },
-    {
-      "boot": "3.2.12",
-      "framework": "6.1.15",
-      "java": "21"
-    },
-    {
-      "boot": "3.3.12",
-      "framework": "6.1.20",
-      "java": "17"
-    },
-    {
-      "boot": "3.3.12",
-      "framework": "6.1.20",
-      "java": "21"
-    },
     {
       "boot": "3.4.6",
       "framework": "6.2.7",