Change ITensorGaussianMPS URL

[mtfishman]

Similar to #105961, I followed the Github documentation guide to splitting a subfolder out into a new repository, and then I checked that the new repository contains all registered versions of the package:

julia> check_package_versions("ITensorGaussianMPS", "https://github.com/ITensor/ITensorGaussianMPS.jl.git")
Cloning into '/var/folders/qz/q22pzwm144z9fq57mpf1hfp40000gq/T/jl_Lzws5o'...
remote: Enumerating objects: 237, done.
remote: Counting objects: 100% (237/237), done.
remote: Compressing objects: 100% (106/106), done.
remote: Total 237 (delta 128), reused 236 (delta 127), pack-reused 0
Receiving objects: 100% (237/237), 80.22 KiB | 20.05 MiB/s, done.
Resolving deltas: 100% (128/128), done.
ITensorGaussianMPS: v0.0.1 found
ITensorGaussianMPS: v0.0.2 found
ITensorGaussianMPS: v0.0.3 found
ITensorGaussianMPS: v0.0.4 found
ITensorGaussianMPS: v0.0.5 found
ITensorGaussianMPS: v0.1.0 found
ITensorGaussianMPS: v0.1.1 found
ITensorGaussianMPS: v0.1.2 found
ITensorGaussianMPS: v0.1.3 found
ITensorGaussianMPS: v0.1.4 found
ITensorGaussianMPS: v0.1.5 found
ITensorGaussianMPS: v0.1.6 found
12-element Vector{@NamedTuple{pkg_name::String, version::VersionNumber, found::Bool}}:
 (pkg_name = "ITensorGaussianMPS", version = v"0.0.1", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.0.2", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.0.3", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.0.4", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.0.5", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.0", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.1", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.2", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.3", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.4", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.5", found = 1)
 (pkg_name = "ITensorGaussianMPS", version = v"0.1.6", found = 1)

[mtfishman]

Thanks @ericphanson!