fix(github-release): update cilium-source to v1.15.6

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
cilium-source	patch	v1.15.5 -> v1.15.6

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Release Notes

cilium/cilium (cilium-source)

### [`v1.15.6`](https://togithub.com/cilium/cilium/compare/1.15.6...1.15.6) [Compare Source](https://togithub.com/cilium/cilium/compare/1.15.6...1.15.6) ### [`v1.15.6`](https://togithub.com/cilium/cilium/compare/1.15.5...1.15.6) [Compare Source](https://togithub.com/cilium/cilium/compare/1.15.5...1.15.6)

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Configuration

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