fix: ignore local feeds in NuGet config (#6348)

...uget/__fixtures__/multiple-package-files/one/NuGet.config

.../nuget/__fixtures__/multiple-package-files/one/one.csproj

...uget/__fixtures__/multiple-package-files/two/NuGet.config

.../nuget/__fixtures__/multiple-package-files/two/two.csproj

.../__fixtures__/with-local-feed-in-config-file/NuGet.config

...feed-in-config-file/with-local-feed-in-config-file.csproj

lib/manager/nuget/__snapshots__/extract.spec.ts.snap

lib/manager/nuget/extract.spec.ts

lib/manager/nuget/extract.ts