Replace MyGet with Feedz as our nightly package repository.

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

MyGet is refusing to upload our binaries reporting the following error

Pushing SixLabors.ImageSharp.3.0.0-alpha.0.101.nupkg to 'https://www.myget.org/F/sixlabors/api/v2/package'...
PUT https://www.myget.org/F/sixlabors/api/v2/package/
RequestEntityTooLarge https://www.myget.org/F/sixlabors/api/v2/package/ 1312ms
error: Response status code does not indicate success: 413 (The total packages size for the pending uploads is too large. The feed owner may have to upgrade the MyGet subscription to resolve this issue.).

We've only used 6MB of 100MB so I'm switching our as I cannot afford time wasted.

Feedz give us 2GB of storage and 2GB of package traffic per month plus has a limit of 3.5GB for individual package sizes so should never cause issues.