Silence noisy test in test/cmdlineargs.jl (JuliaLang#52225)

This is spamming
([example](https://buildkite.com/julialang/julia-master/builds/30247#018be235-0cd3-43bb-ba43-cc378ac0d682/792-1056))
```
      From worker 12:	ERROR: LoadError: UndefVarError: `@which` not defined in `Main`
      From worker 12:	Stacktrace:
      From worker 12:	 [1] top-level scope
      From worker 12:	   @ :0
      From worker 12:	 [2] lower
      From worker 12:	   @ ./meta.jl:163 [inlined]
      From worker 12:	 [3] eval_user_input(errio::IOContext{Base.PipeEndpoint}, ast::Any, show_value::Bool)
      From worker 12:	   @ Base ./client.jl:141
      From worker 12:	 [4] run_main_repl(interactive::Bool, quiet::Bool, banner::Symbol, history_file::Bool, color_set::Bool)
      From worker 12:	   @ Base ./client.jl:477
      From worker 12:	 [5] repl_main
      From worker 12:	   @ Base ./client.jl:561 [inlined]
      From worker 12:	 [6] _start()
      From worker 12:	   @ Base ./client.jl:535
      From worker 12:	in expression starting at none:1
```
in all jobs

test/cmdlineargs.jl

@@ -4,8 +4,8 @@ import Libdl
 
 # helper function for passing input to stdin
 # and returning the stdout result
-function writereadpipeline(input, exename)
- p = open(exename, "w+")
+function writereadpipeline(input, exename; stderr=nothing)
+ p = open(pipeline(exename; stderr), "w+")
  @async begin
  write(p.in, input)
  close(p.in)
@@ -145,14 +145,19 @@ end
 
 let exename = `$(Base.julia_cmd()) --startup-file=no --color=no`
  # tests for handling of ENV errors
- let v = writereadpipeline(
+ let
+ io = IOBuffer()
+ v = writereadpipeline(
  "println(\"REPL: \", @which(less), @isdefined(InteractiveUtils))",
  setenv(`$exename -i -E '@assert isempty(LOAD_PATH); push!(LOAD_PATH, "@stdlib"); @isdefined InteractiveUtils'`,
  "JULIA_LOAD_PATH" => "",
  "JULIA_DEPOT_PATH" => ";:",
- "HOME" => homedir()))
+ "HOME" => homedir());
+ stderr=io)
  # @which is undefined
  @test_broken v == ("false\nREPL: InteractiveUtilstrue\n", true)
+ stderr = String(take!(io))
+ @test_broken isempty(stderr)
  end
  let v = writereadpipeline("println(\"REPL: \", InteractiveUtils)",
  setenv(`$exename -i -e 'const InteractiveUtils = 3'`,