Bump gfx-backend-dx11 from 0.6.0 to 0.6.15
Bump gfx-backend-dx11 from 0.6.0 to 0.6.15

Bumps [gfx-backend-dx11](https://github.com/gfx-rs/gfx) from 0.6.0 to 0.6.15.
- [Release notes](https://github.com/gfx-rs/gfx/releases)
- [Changelog](https://github.com/gfx-rs/gfx/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gfx-rs/gfx/commits)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>

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