chore(deps): update dependency add-to-calendar-button to v2.6.15

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
add-to-calendar-button (source)	2.6.14 -> 2.6.15

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Release Notes

add2cal/add-to-calendar-button (add-to-calendar-button)

### [`v2.6.15`](https://togithub.com/add2cal/add-to-calendar-button/releases/tag/v2.6.15) [Compare Source](https://togithub.com/add2cal/add-to-calendar-button/compare/v2.6.14...v2.6.15) - Workaround to make all-day events with Yahoo work again. - Demo page optimization.

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Configuration

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