fix(deps): update dependency koa to v2.15.3

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
koa	2.15.2 -> 2.15.3

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Release Notes

koajs/koa (koa)

### [`v2.15.3`](https://togithub.com/koajs/koa/compare/2.15.2...77cbf2e47ea7067c937b0f21ea0aa4fb73bac115) [Compare Source](https://togithub.com/koajs/koa/compare/2.15.2...2.15.3)

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