[R] Update docs about applicability of `learning_rate` #11503

Job	Run time
Build libxgboost4j.so with CUDA	5m 57s
Build libxgboost4j.dylib for MacOS (Apple Silicon)	1m 42s
Build libxgboost4j.so targeting glibc 2.17 (arch aarch64, runner linux-arm64-cpu)	1m 43s
Build libxgboost4j.dylib for MacOS (Intel)	3m 53s
Build and test JVM packages (Linux, Scala 2.12)	10m 32s
Build libxgboost4j.so targeting glibc 2.17 (arch x86_64, runner linux-amd64-cpu)	1m 51s
Build and test JVM packages (Linux, Scala 2.13)	4m 53s
Build and test JVM packages (windows-latest)	8m 37s
Build and test JVM packages (macos-13)	14m 14s
Build docs for JVM packages	4m 46s
Test JVM packages with CUDA (Scala 2.12)	6m 12s
Test JVM packages with CUDA (Scala 2.13)	6m 9s
Deploy JVM packages to S3 (cpu)	9s
Deploy JVM packages to S3 (cpu)	9s
Deploy JVM packages to S3 (gpu)	10s
Deploy JVM packages to S3 (gpu)	7s
	1h 11m 4s

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