Upgrade to Spring LDAP 2.3.4.RELEASE

There's no date yet, but when it's available we should remove [`--add-exports=java.naming/com.sun.jndi.ldap=ALL-UNNAMED`](https://github.com/spring-projects/spring-boot/blob/d82daa4f839dd5c88413788d5898b76dcb420ec9/buildSrc/src/main/java/org/springframework/boot/build/toolchain/ToolchainPlugin.java#L89) from test tasks' JVM args in 2.4 and 2.5 when we forward-merge the upgrade.