Bump ext/SDL from d5f0773 to b42cb1c

Bumps [ext/SDL](https://github.com/libsdl-org/SDL) from `d5f0773` to `b42cb1c`.
- [Release notes](https://github.com/libsdl-org/SDL/releases)
- [Commits](libsdl-org/SDL@d5f0773...b42cb1c)

---
updated-dependencies:
- dependency-name: ext/SDL
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>