Make relocatedepot test more robust (JuliaLang#53110)

As discussed in the `#ci-dev` call (see
JuliaLang#53103 (comment)
and
JuliaLang#53104 (comment))
there were two problems:

* the use of `Base.require` caused the package to be loaded
* the name of the package was a generic placeholder, and clashed with
other packages loaded during the tests called with the same generic
name.

The solution was to rename test module with a more specific name, and
replace `Base.require` with `Base.compilecache`, the latter only
compiles the package without loading it.

Should fix JuliaLang#53103, close JuliaLang#53104.

test/relocatedepot.jl

@@ -145,9 +145,9 @@ if !test_relocated_depot
  Base.require(pkg)
  mktempdir() do depot3
  # precompile Foo in depot3
- open(joinpath(depot3, "Foo.jl"), write=true) do io
+ open(joinpath(depot3, "Module52161.jl"), write=true) do io
  println(io, """
- module Foo
+ module Module52161
  using Example1
  using Example2
  srcfile1 = joinpath(pkgdir(Example1), "src", "Example1.jl")
@@ -159,13 +159,13 @@ if !test_relocated_depot
  end
  pushfirst!(LOAD_PATH, depot3)
  pushfirst!(DEPOT_PATH, depot3)
- pkg = Base.identify_package("Foo")
- Base.require(pkg)
+ pkg = Base.identify_package("Module52161")
+ Base.compilecache(pkg)
  cachefile = joinpath(depot3, "compiled",
- "v$(VERSION.major).$(VERSION.minor)", "Foo.ji")
+ "v$(VERSION.major).$(VERSION.minor)", "Module52161.ji")
  _, (deps, _, _), _... = Base.parse_cache_header(cachefile)
  @test map(x -> x.filename, deps) ==
- [ joinpath(depot3, "Foo.jl"),
+ [ joinpath(depot3, "Module52161.jl"),
  joinpath(depot1, "Example1", "src", "Example1.jl"),
  joinpath(depot2, "Example2", "src", "Example2.jl") ]
  end