Update qemux/qemu-docker Docker tag to v5.15

[balena-renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
qemux/qemu-docker	final	minor	5.14 -> 5.15

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Release Notes

qemus/qemu-docker (qemux/qemu-docker)

### [`v5.15`](https://togithub.com/qemus/qemu-docker/releases/tag/v5.15) [Compare Source](https://togithub.com/qemus/qemu-docker/compare/v5.14...v5.15) #### What's Changed - feat: Support download of disk images by [@​kroese](https://togithub.com/kroese) in [https://github.com/qemus/qemu-docker/pull/560](https://togithub.com/qemus/qemu-docker/pull/560) **Full Changelog**: https://github.com/qemus/qemu-docker/compare/v5.14...v5.15

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