Configure dependabot to only propose logback patch versions

Since logback 1.4.x requires Java 11

https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/controlling-dependencies-updated#specifying-the-semantic-versioning-level-to-ignore

Author: raboof

.github/dependabot.yml

@@ -20,6 +20,10 @@ updates:
     schedule:
       interval: "weekly"
       day: "friday"
+    ignore:
+      # post-1.3 versions require Java 11
+      - dependency-name: "ch.qos.logback:logback-*"
+        versions: "[1.4,)"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: