Bump org.apache.rat:apache-rat from 0.13 to 0.15 in /buildSrc

Bumps org.apache.rat:apache-rat from 0.13 to 0.15.

---
updated-dependencies:
- dependency-name: org.apache.rat:apache-rat
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

buildSrc/build.gradle

@@ -69,7 +69,7 @@ dependencies {
     compileOnly localGroovy()
 
     // Required for dependency licenses task
-    implementation 'org.apache.rat:apache-rat:0.13'
+    implementation 'org.apache.rat:apache-rat:0.15'
     implementation 'commons-codec:commons-codec:1.15'
 
     if (localRepo) {