Log Message:
schismtracker: update to 20220506.

Summary of changes since 20220125 release:

- Distribute the latest development version of SDL 1.2 with macOS builds of
  Schism Tracker instead of the latest release version, fixing "Failed to
  start CoreAudio" errors on recent macOS versions
- Fix import of EBF volume slides from MOD/XM files
- Fix various multisample instrument bugs
- Fix out-of-bounds memory access in display scaling code (only an issue in
  some display implementations)