Catching string `yanked` in RegistryCI

https://github.com/JuliaRegistries/General/pull/137817 needed to be followed up with https://github.com/JuliaRegistries/General/pull/137826 because `yanked = "true"` led to issues like: ``` ERROR: TypeError: non-boolean (String) used in boolean context Stacktrace: [1] (::Pkg.Registry.var"#9#14")(::Pair{String, Any}) @ Pkg.Registry ./none:0 [2] iterate @ ./generator.jl:48 [inlined] [3] Dict{VersionNumber, Pkg.Registry.VersionInfo}(kv::Base.Generator{Dict{String, Any}, Pkg.Registry.var"#9#14"}) @ Base ./dict.jl:95 [4] init_package_info!(pkg::Pkg.Registry.PkgEntry) @ Pkg.Registry ~/.julia/juliaup/julia-1.11.6+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/Pkg/src/Registry/registry_instance.jl:200 [5] registry_info @ ~/.julia/juliaup/julia-1.11.6+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/Pkg/src/Registry/registry_instance.jl:184 [inlined] ... ``` The true issue though is that the Registry CI did not catch this, i.e. it gave all green check marks and everything passed the registry consistency checks, so I had merged thinking it was fine. To prevent this issue in the future, the consistency checks should ensure that any `yanked` values are boolean. Though I'm not sure why the registry consistency checks were able to pass without this, because adding a package while this was in the registry seemed to just error any package downstream 😅 , so things should've failed. Something about yanking has a blind spot though.