Bump @backstage/plugin-proxy-backend from 0.4.2 to 0.4.4 in /backstage

Bumps [@backstage/plugin-proxy-backend](https://github.com/backstage/backstage/tree/HEAD/plugins/proxy-backend) from 0.4.2 to 0.4.4.
- [Release notes](https://github.com/backstage/backstage/releases)
- [Changelog](https://github.com/backstage/backstage/blob/master/plugins/proxy-backend/CHANGELOG.md)
- [Commits](https://github.com/backstage/backstage/commits/v0.4.4/plugins/proxy-backend)

---
updated-dependencies:
- dependency-name: "@backstage/plugin-proxy-backend"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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