prevent precompilation from breaking if Base.PkgId is imported

[KristofferC]

Problem:

julia> using Base: PkgId

julia> using Example
[ Info: Precompiling Example [7876af07-990d-54b4-ab0e-23690620f79a]
ERROR: UndefVarError: PkgId not defined
Stacktrace:
 [1] top-level scope
   @ none:1
 [2] eval
   @ ./boot.jl:368 [inlined]
 [3] eval(x::Expr)
   @ Base.MainInclude ./client.jl:453
 [4] top-level scope
   @ none:1
ERROR: Failed to precompile Example [7876af07-990d-54b4-ab0e-23690620f79a] to /home/kc/.julia/compiled/v1.8/Example/jl_lTKLYS.
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:33
 [2] compilecache(pkg::PkgId, path::String, internal_stderr::IO, internal_stdout::IO, ignore_loaded_modules::Bool)
   @ Base ./loading.jl:1483
 [3] compilecache(pkg::PkgId, path::String)
   @ Base ./loading.jl:1427
 [4] _require(pkg::PkgId)
   @ Base ./loading.jl:1137
 [5] require(uuidkey::PkgId)
   @ Base ./loading.jl:1030
 [6] require(into::Module, mod::Symbol)
   @ Base ./loading.jl:1014

repr will only print a module prefix if the symbol is not existing in Main but the module prefix is unconditionally needed here since the code will be evaluated in another process.

Fixes #40888

[JeffBezanson]

Great example of #29466...