Recent regression in spurious invalidations.

[KristofferC]

Running with Pkg out of the sysimage (using this commit 412c8f4) and the following Pkg commit JuliaLang/Pkg.jl@f2d8b64 there is a recent regression where the precompilation workload in Pkg seems to get heavily invalidated and becomes basically worthless:

# Good
julia> @time Pkg.add("Example")
...
  1.735661 seconds (3.62 M allocations: 237.936 MiB, 7.02% gc time, 45.09% compilation time)

# Bad
julia> @time Pkg.add("Example")
...
 11.234634 seconds (4.29 M allocations: 307.999 MiB, 91.73% compilation time: 73% of which was recompilation)

This recompilation seems spurious since there are no (AFAIK) other packages getting loaded that would cause this.

This was bisected to #51036 cc @vtjnash

Marking for 1.10 since the offending commit is marked for backporting.