[release-v1.17][npm]: Bump @backstage/plugin-app-backend (#802)

Bumps [@backstage/plugin-app-backend](https://github.com/backstage/backstage/tree/HEAD/plugins/app-backend) from 0.3.76 to 0.5.6.
- [Release notes](https://github.com/backstage/backstage/releases)
- [Changelog](https://github.com/backstage/backstage/blob/master/plugins/app-backend/CHANGELOG.md)
- [Commits](https://github.com/backstage/backstage/commits/HEAD/plugins/app-backend)

---
updated-dependencies:
- dependency-name: "@backstage/plugin-app-backend"
  dependency-version: 0.5.6
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backstage/packages/backend/package.json

@@ -21,7 +21,7 @@
     "@backstage/catalog-client": "^1.4.6",
     "@backstage/catalog-model": "^1.4.3",
     "@backstage/config": "^1.1.1",
-    "@backstage/plugin-app-backend": "^0.3.55",
+    "@backstage/plugin-app-backend": "^0.5.6",
     "@backstage/plugin-auth-backend": "^0.20.0",
     "@backstage/plugin-auth-node": "^0.4.1",
     "@backstage/plugin-catalog-backend": "^1.15.0",