fix(deps) dependabot ignore junit.platform updates > 6.0.0, group junit

junit-platform-launcher > 6 dropped Java 8 support.
Also group junit updates to reduce dependabot PR amount.

Author: cgoetz-inovex

.github/dependabot.yml

@@ -15,6 +15,11 @@ updates:
         versions: ["[6.0.0,)"]
       - dependency-name: "org.junit.jupiter:junit-jupiter-engine"
         versions: ["[6.0.0,)"]
+      - dependency-name: "org.junit.platform:junit-platform-launcher"
+        versions: ["[6.0.0,)"]
+    groups:
+      junit:
+        patterns: ["org.junit.*"]
     cooldown:
         default-days: 7
         exclude: ["cloud.stackit*"]