macOS CI R jobs fail

[StrikerRUS]

Can be observed in #3874.
Refer to https://github.com/microsoft/LightGBM/pull/3874/checks?check_run_id=1784106648

* checking tests ...
  Running ‘testthat.R’
 � ERROR
Running the tests in ‘tests/testthat.R’ failed.
Complete output:
  > library(testthat)
  > library(lightgbm)
  Loading required package: R6
  > 
  > test_check(
  +     package = "lightgbm"
  +     , stop_on_failure = TRUE
  +     , stop_on_warning = FALSE
  + )
  Error in loadNamespace(name) : there is no package called 'withr'
  Calls: test_check ... loadNamespace -> withRestarts -> withOneRestart -> doWithOneRestart
  Execution halted

[StrikerRUS]

cc @jameslamb

[jameslamb]

ah! will look right now

[StrikerRUS]

Only R 4.x both CRAN and CMake jobs are affected.

[github-actions]

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