Bump log4j-core from 2.13.2 to 2.15.0

Bumps log4j-core from 2.13.2 to 2.15.0.

---
updated-dependencies:
- dependency-name: org.apache.logging.log4j:log4j-core
  dependency-type: direct:development
...

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

Author: dependabot[bot]

pom.xml

@@ -47,7 +47,7 @@
     <javax.annotation.version>1.3.2</javax.annotation.version>
 
     <!-- For testing only. -->
-    <log4j.version>2.7</log4j.version>
+    <log4j.version>2.15.0</log4j.version>
     <hamcrest.optional>1.0</hamcrest.optional>
   </properties>