Private Repository Causes Bitrise Auth issues

[3SC-Bitrise]

The Bitrise Xcode Test step is failing with log

xcodebuild encountered an error (74): 
- Could not resolve package dependencies:
  Failed to clone repository https://github.com/3sidedcube/ArcUI.git:
    Cloning into bare repository '/Users/vagrant/Library/Developer/Xcode/DerivedData/.../ArcUI-ce55e926'...
    fatal: could not read Username for 'https://github.com': terminal prompts disabled

As documented by Bitrise, private repositories need to be accessed with

git@github.com:3sidedcube/ArcUI.git

instead of

https://github.com/3sidedcube/ArcUI.git

but when adding that as a swift package in Xcode, this yields the attached error.

The temporary fix is to make this a public repo.
There's nothing sensitive so it is OK, but private would be preferred.

Other resources:

• Bitrise Link
• SPM Bitrise Issue