prevent `package_callbacks` to run multiple time for a single package

[KristofferC]

Introduced in https://github.com/JuliaLang/julia/pull/52841.

[topolarity]

Should this keep track of which packages have had their callbacks run somewhere, so that we can assert they are run exactly once?

[KristofferC]

That's kind of what this does, no? I'll merge for now at least.