string_concatenation_hint_handler fails tests

[vtjnash]

Apparent regression in tests from merging #45823 recently?

      From worker 10:	┌ Error: Hint-handler string_concatenation_hint_handler for MethodError in Base caused an error
      From worker 10:	└ @ Base.Experimental experimental.jl:321
missing                                         (10) |    42.50 |   0.30 |  0.7 |     704.53 |  2004.57

These register_error_hint should probably be going into REPL or InteractiveUtils; they probably should not be going into Base.

Originally posted by @vtjnash in #45823 (comment)

[KristofferC]

cc @merryhime, maybe you can look at this?

[merryhime]

hey, will do when i can.