macOS: Disabled & failing ResizeWithBoxPadMode tests

[antonfirsov]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

Description

The tests disabled in #1424 fail on macOS. This is likely a product bug.

Steps to Reproduce

Enable the tests and run them on macOS.

System Configuration

• ImageSharp version: current master
• Other ImageSharp packages and versions: -
• Environment (Operating system, version and so on): macOS on GH CI
• .NET Framework version: .NET Core 3.1
• Additional information: -

[antonfirsov]

Fixed by #1434.