Bump log4jVersion from 2.20.0 to 2.21.0

Bumps `log4jVersion` from 2.20.0 to 2.21.0.

Updates `org.apache.logging.log4j:log4j-core` from 2.20.0 to 2.21.0

Updates `org.apache.logging.log4j:log4j-jcl` from 2.20.0 to 2.21.0

Updates `org.apache.logging.log4j:log4j-slf4j2-impl` from 2.20.0 to 2.21.0

---
updated-dependencies:
- dependency-name: org.apache.logging.log4j:log4j-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-jcl
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-slf4j2-impl
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

build.gradle

@@ -5,7 +5,7 @@ buildscript {
         junit5PlatformVersion = '1.10.0'
 
         slf4jVersion = '2.0.7' // http://www.slf4j.org/download.html
-        log4jVersion = '2.20.0' // https://logging.apache.org/log4j/2.x/javadoc.html
+        log4jVersion = '2.21.0' // https://logging.apache.org/log4j/2.x/javadoc.html
         // Note: Since Jackson 2.14, Android SDK 26 is required
         // https://github.com/FasterXML/jackson/wiki/Jackson-Releases
         jacksonVersion = '2.15.2' // https://github.com/FasterXML/jackson-databind/tags