Support `Pkg.test`'s keyword parameter `allow_reresolve`

[jakobjpeters]

Pkg.test uses:

allow_reresolve::Bool=true: allow Pkg to reresolve the package versions in the test environment

Since I am caching precompiled dependencies in CI, I want to set allow_reresolve = false to prevent unnecessary precompilation.

[kleinschmidt]

Just came here to request the same thing!

[kleinschmidt]

From poking around a bit, it seems like most of the action actually happens in TestEnv, since that's what TestReports leans on to actually instantiate and active the test environment. So might be a feature request there...as far as I can tell it tries not to re-resolve things though!

[kleinschmidt]

Oh wait it already does 🤦. I'll make a PR then.