fix: updates app.js for the handling of an error being thrown by the verify method in webhooks.js

[nickfloyd]

Relates to:

• https://github.com/octokit/app.js/pull/482
• https://github.com/octokit/webhooks.js/pull/914
• https://github.com/octokit/webhooks.js/pull/915
• https://github.com/octokit/webhooks.js/pull/916
• https://github.com/octokit/webhooks.js/pull/917

Fixes an issue where webhooks.js was throwing an error which could cause downstream problems.

[github-actions[bot]]

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[github-actions[bot]]

:tada: This PR is included in version 3.1.2 :tada:

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

Your semantic-release bot :package::rocket:

[batflarrow]

Hello, Can we backport this fix to v2 as well? Happy to open a pr as well.