Revise tests clones general registry which is quite slow

[KristofferC]

When running the Revise tests I see:

  Activating new project at `C:\Users\KRISTO~1\AppData\Local\Temp\jl_6nmNSw`
  Generating  project TestPackage:
    TestPackage\Project.toml
    TestPackage\src\TestPackage.jl
vvvvvvvvvvvvvvvvvvvvv
  Installing known registries into `C:\Users\Kristoffer\.julia`
     Cloning registry from "https://github.com/JuliaRegistries/General.git"
       Added registry `General` to `C:\Users\Kristoffer\.julia\registries\General`
^^^^^^^^^^^^^^^^^^
     Cloning git-repo `C:\Users\Kristoffer\AppData\Local\Temp\jl_vx8FqQ\TestPackage`
    Updating git-repo `C:\Users\Kristoffer\AppData\Local\Temp\jl_vx8FqQ\TestPackage`
    Updating registry at `C:\Users\Kristoffer\.julia\registries\General`
┌ Info: The General registry is installed via git. Consider reinstalling it via
│ the newer faster direct from tarball format by running:
│   pkg> registry rm General; registry add General
└ 
    Updating git-repo `https://github.com/JuliaRegistries/General.git`

This is a little bit ironic considering

Revise.jl/test/runtests.jl

Line 3058 in d21c32f

# Skip cloning the General registry since that is slow and unnecessary