Bump redox_syscall from 0.2.13 to 0.2.15 in /src/rust (#7446)

Bumps redox_syscall from 0.2.13 to 0.2.15.

---
updated-dependencies:
- dependency-name: redox_syscall
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]