fix(deps): update rust crate icalendar to 0.15.6

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
icalendar	dependencies	patch	0.15.4 -> 0.15.6

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Release Notes

hoodie/icalendar-rs (icalendar)

### [`v0.15.6`](https://togithub.com/hoodie/icalendar-rs/blob/HEAD/CHANGELOG.md#v0156-2023-07-22) [Compare Source](https://togithub.com/hoodie/icalendar-rs/compare/v0.15.5...v0.15.6) ##### Fixes - **deps:** update rust crate chrono-tz to 0.8.3 ([1a31f9a](https://togithub.com/hoodie/icalendar-rs/commit/1a31f9a0bad05905db2e381b6e592f44cb0ee817)) ### [`v0.15.5`](https://togithub.com/hoodie/icalendar-rs/blob/HEAD/CHANGELOG.md#v0155-2023-07-21) [Compare Source](https://togithub.com/hoodie/icalendar-rs/compare/v0.15.4...v0.15.5) ##### Features - add wasm support ([336dee7](https://togithub.com/hoodie/icalendar-rs/commit/336dee785da9a9763c854731893f6877a763a9c2))

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