chore(deps): update dependency @octokit/app to v15 (#162)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [@octokit/app](https://togithub.com/octokit/app.js) | [`^14.0.0` ->
`^15.0.0`](https://renovatebot.com/diffs/npm/@octokit%2fapp/14.0.0/15.0.1)
|
[![age](https://developer.mend.io/api/mc/badges/age/npm/@octokit%2fapp/15.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/@octokit%2fapp/15.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/@octokit%2fapp/14.0.0/15.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@octokit%2fapp/14.0.0/15.0.1?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>octokit/app.js (@&#8203;octokit/app)</summary>

###
[`v15.0.1`](https://togithub.com/octokit/app.js/releases/tag/v15.0.1)

[Compare
Source](https://togithub.com/octokit/app.js/compare/v15.0.0...v15.0.1)

##### Bug Fixes

- **types:** export minimal types required for the `App` class
([#&#8203;536](https://togithub.com/octokit/app.js/issues/536))
([318e6fd](https://togithub.com/octokit/app.js/commit/318e6fd85a931079b383bbe3f6d8960ed9831b78))

###
[`v15.0.0`](https://togithub.com/octokit/app.js/releases/tag/v15.0.0)

[Compare
Source](https://togithub.com/octokit/app.js/compare/v14.1.0...v15.0.0)

##### Features

- package is now ESM
([#&#8203;512](https://togithub.com/octokit/app.js/issues/512))
([ea347ff](https://togithub.com/octokit/app.js/commit/ea347ffc27402e5b6f43e48ad6f7ab31645d7275))

##### BREAKING CHANGES

-   package is now ESM

###
[`v14.1.0`](https://togithub.com/octokit/app.js/releases/tag/v14.1.0)

[Compare
Source](https://togithub.com/octokit/app.js/compare/v14.0.2...v14.1.0)

##### Features

- **security:** Add provenance
([#&#8203;528](https://togithub.com/octokit/app.js/issues/528))
([6860c97](https://togithub.com/octokit/app.js/commit/6860c97493b8b68446a49fbece0f2d86ab17a5c6))

###
[`v14.0.2`](https://togithub.com/octokit/app.js/releases/tag/v14.0.2)

[Compare
Source](https://togithub.com/octokit/app.js/compare/v14.0.1...v14.0.2)

##### Bug Fixes

- update for the handling of an error being thrown by the verify method
in webhooks.js
([#&#8203;482](https://togithub.com/octokit/app.js/issues/482))
([b59444d](https://togithub.com/octokit/app.js/commit/b59444d7f07146fb1abd203b19b6684401622dc0))

###
[`v14.0.1`](https://togithub.com/octokit/app.js/releases/tag/v14.0.1)

[Compare
Source](https://togithub.com/octokit/app.js/compare/v14.0.0...v14.0.1)

##### Bug Fixes

- **deps:** update octokit monorepo (major)
([#&#8203;469](https://togithub.com/octokit/app.js/issues/469))
([6d51289](https://togithub.com/octokit/app.js/commit/6d51289448793cc76a3fcd4339b4aa0eb746c4b9))

</details>

---

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