build(deps-dev): bump @firebase/app from 0.6.21 to 0.6.26 (#1329)

Bumps [@firebase/app](https://github.com/firebase/firebase-js-sdk/tree/HEAD/packages/app) from 0.6.21 to 0.6.26.
- [Release notes](https://github.com/firebase/firebase-js-sdk/releases)
- [Changelog](https://github.com/firebase/firebase-js-sdk/blob/@firebase/[email protected]/packages/app/CHANGELOG.md)
- [Commits](https://github.com/firebase/firebase-js-sdk/commits/@firebase/[email protected]/packages/app)

---
updated-dependencies:
- dependency-name: "@firebase/app"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]