`.onload()` of {styler} causes error

[lorenzwalthert]

> ask_to_switch_to_non_default_cache_root()
# Error in vapply(X, FUN, FUN.VALUE = character(1), ..., USE.NAMES = USE.NAMES) : 
#values must be length 1,
#but FUN(X[[1]]) result is length 9

[lorenzwalthert]

Belongs to the 10% of the code not tested and broken only last month with https://github.com/r-lib/cli/releases/tag/v3.1.0.