Handle registrying things that don't support the version of julia that the CI is running

[oxinabox]

Right now Automerge runs julika 1.6
If you register a package release that only supporst say 1.0 or 1.7
then it will fail with

* I was not able to install the package (i.e. `Pkg.add("TestEnv")` failed). See the CI logs for details.

* I was not able to load the package (i.e. `import TestEnv` failed). See the CI logs for details.

E.g JuliaRegistries/General#42120

The ideal thing to do would be to make sure the CI was running the right version.
Probably an OK thing to do would be to just auto-pass those tests.
It is unusual for someone not to support the current release of julia
and anyone who does probably knows what they are doing.

[oxinabox]

A extra challenging case is if a package says it supports say julia ^1.0
but it depends on some package that only supports ~1.3
then that really should be tested on 1.3.
but can't work that out without actually resolving the dependencies

[DilumAluthge]

I don't think we should auto-pass, necessarily. Probably the best thing to do is to figure out what Julia version is needed, and run Pkg.add and import checks against that.

[oxinabox]

I don't think we should auto-pass, necessarily. Probably the best thing to do is to figure out what Julia version is needed, and run Pkg.add and import checks against that.

I agree that is the best thing.
But it sounds hard, and may be harder than it is worth.
but otoh maybe it is easier than i think

[oxinabox]

Sadly, Pkg does not throw a rich exception type that we can just read the information from

julia> try
       Pkg.add("Diffractor")
       catch e
       global err
       err=e
       end
   Resolving package versions...
Pkg.Resolve.ResolverError("Unsatisfiable requirements detected for package \e[38;5;75mDiffractor [9f5e2b26]\e[39m:\n \e[38;5;75mDiffractor [9f5e2b26]\e[39m log:\n ├─possible versions are: \e[38;5;75m0.2.0-0.2.1\e[39m or uninstalled\n ├─restricted to versions \e[38;5;75m*\e[39m by an explicit requirement, leaving only versions: \e[38;5;75m0.2.0-0.2.1\e[39m\n └─restricted by julia compatibility requirements to versions: uninstalled — no versions left", nothing)

julia> err
Pkg.Resolve.ResolverError("Unsatisfiable requirements detected for package \e[38;5;75mDiffractor [9f5e2b26]\e[39m:\n \e[38;5;75mDiffractor [9f5e2b26]\e[39m log:\n ├─possible versions are: \e[38;5;75m0.2.0-0.2.1\e[39m or uninstalled\n ├─restricted to versions \e[38;5;75m*\e[39m by an explicit requirement, leaving only versions: \e[38;5;75m0.2.0-0.2.1\e[39m\n └─restricted by julia compatibility requirements to versions: uninstalled — no versions left", nothing)

julia> err.
ex   msg
julia> err.ex

julia> err.msg
"Unsatisfiable requirements detected for package \e[38;5;75mDiffractor [9f5e2b26]\e[39m:\n \e[38;5;75mDiffractor [9f5e2b26]\e[39m log:\n ├─possible versions are: \e[38;5;75m0.2.0-0.2.1\e[39m or uninstalled\n ├─restricted to versions \e[38;5;75m*\e[39m by an explicit requirement, leaving only versions: \e[38;5;75m0.2.0-0.2.1\e[39m\n └─restricted by julia compatibility requirements to versions: uninstalled — no versions left"

Maybe as a basic good enough approach we could just check err isa ResolverError && contains(err.msg, "restricted by julia compatibility requirements")