Bump com.diffplug.spotless from 6.12.1 to 6.13.0 in /java (aws-observability#421)

Bumps com.diffplug.spotless from 6.12.1 to 6.13.0.

---
updated-dependencies:
- dependency-name: com.diffplug.spotless
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

java/settings.gradle.kts

@@ -1,6 +1,6 @@
 pluginManagement {
     plugins {
-        id("com.diffplug.spotless") version "6.12.1"
+        id("com.diffplug.spotless") version "6.13.0"
         id("com.github.ben-manes.versions") version "0.44.0"
         id("com.github.johnrengelman.shadow") version "7.1.2"
     }