Siesta currently fails when added as a SwiftPM dependency using a version number instead of a branch (see #308), because:

• Siesta uses an unmerged feature branch on a fork of Quick,
• Siesta specifies that branch instead of a version number in its dependency on Quick,
• SwiftPM doesn’t allow a versioned dependency (e.g. “Siesta ≥1.5.0”) to have a branch-based dependency, and
• SwiftPM doesn’t know how to ignore test-only targets of dependencies.

This PR fixes the issue by using a newly created ad hoc version number for the pcantrell fork of Quick until Quick/Quick#820 is merged.