Bump log4j.version from 2.19.0 to 2.20.0 in /core (closes #529)

Bumps `log4j.version` from 2.19.0 to 2.20.0.

Updates `log4j-api` from 2.19.0 to 2.20.0
- [Release notes](https://github.com/apache/logging-log4j2/releases)
- [Changelog](https://github.com/apache/logging-log4j2/blob/release-2.x/CHANGELOG.adoc)
- [Commits](https://github.com/apache/logging-log4j2/compare/rel/2.19.0...rel/2.20.0)

Updates `log4j-core` from 2.19.0 to 2.20.0
- [Release notes](https://github.com/apache/logging-log4j2/releases)
- [Changelog](https://github.com/apache/logging-log4j2/blob/release-2.x/CHANGELOG.adoc)
- [Commits](https://github.com/apache/logging-log4j2/compare/rel/2.19.0...rel/2.20.0)

Updates `log4j-slf4j2-impl` from 2.19.0 to 2.20.0
- [Release notes](https://github.com/apache/logging-log4j2/releases)
- [Changelog](https://github.com/apache/logging-log4j2/blob/release-2.x/CHANGELOG.adoc)
- [Commits](https://github.com/apache/logging-log4j2/compare/rel/2.19.0...rel/2.20.0)

Updates `log4j-jul` from 2.19.0 to 2.20.0
- [Release notes](https://github.com/apache/logging-log4j2/releases)
- [Changelog](https://github.com/apache/logging-log4j2/blob/release-2.x/CHANGELOG.adoc)
- [Commits](https://github.com/apache/logging-log4j2/compare/rel/2.19.0...rel/2.20.0)

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

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

Change-Id: Icfa40cc0436592ed202afdfeb7674113046752d0
diff --git a/core/pom.xml b/core/pom.xml
index 5f20cdb..7fb28ad 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -13,7 +13,7 @@
 		<jetty.version>9.4.50.v20221201</jetty.version>
 		<hibernate.version>5.6.15.Final</hibernate.version>
 		<flyway.version>9.15.0</flyway.version>
-		<log4j.version>2.19.0</log4j.version>
+		<log4j.version>2.20.0</log4j.version>
 		<krill.version>[0.61,)</krill.version>
 		<koral.version>[0.39,)</koral.version>
 	</properties>