Bumps [webxr-api](https://github.com/servo/webxr) from `d9ec226` to `3e731ea`.
- [Release notes](https://github.com/servo/webxr/releases)
- [Commits](servo/webxr@d9ec226...3e731ea)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>