Update Rust crate rcgen to 0.12

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
rcgen	dev-dependencies	minor	0.11 -> 0.12
rcgen	dependencies	minor	0.11 -> 0.12

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Release Notes

est31/rcgen (rcgen)

### [`v0.12.0`](https://togithub.com/est31/rcgen/compare/v0.11.3...v0.12.0) [Compare Source](https://togithub.com/est31/rcgen/compare/v0.11.3...v0.12.0) ### [`v0.11.3`](https://togithub.com/est31/rcgen/compare/v0.11.2...v0.11.3) [Compare Source](https://togithub.com/est31/rcgen/compare/v0.11.2...v0.11.3) ### [`v0.11.2`](https://togithub.com/est31/rcgen/compare/v0.11.1...v0.11.2) [Compare Source](https://togithub.com/est31/rcgen/compare/v0.11.1...v0.11.2) ### [`v0.11.1`](https://togithub.com/est31/rcgen/compare/v0.11.0...v0.11.1) [Compare Source](https://togithub.com/est31/rcgen/compare/v0.11.0...v0.11.1)

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