Bump proxy-agent in /appcenter-file-upload-client-node

Bumps [proxy-agent](https://github.com/TooTallNate/proxy-agents/tree/HEAD/packages/proxy-agent) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/TooTallNate/proxy-agents/releases)
- [Changelog](https://github.com/TooTallNate/proxy-agents/blob/main/packages/proxy-agent/CHANGELOG.md)
- [Commits](https://github.com/TooTallNate/proxy-agents/commits/[email protected]/packages/proxy-agent)

---
updated-dependencies:
- dependency-name: proxy-agent
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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