GitHub Actions are all running on Swift 5.2.4

[Samasaur1]

Describe the bug:

Even though specific Swift versions are installed during the GitHub Actions run, they go back to using the Swift version that comes with macOS-latest, which is currently 5.2.4

To Reproduce:

Push a commit, or look here: https://github.com/Samasaur1/DiceKit/runs/831553613

Expected behavior:

That example should be using Swift 4.2.4 (and therefore fail, because I was using function builders.

Implementation Details:

• Development OS: irrelevant
• Target OS: irrelevant
• DiceKit Version 0.21.0

Additional context:

This isn't a problem with the library itself.

[Samasaur1]

Using fwal/swift-setup will fix this issue, although Swift 4.2.4 on macOS doesn't seem to work because it tries to build AppKit for some reason

[Samasaur1]

See this comment: #81 (comment) for more info on Swift 4.2.4