Bump rack-timeout from 0.6.0 to 0.6.3 in /backend (#700)

Bumps [rack-timeout](https://github.com/zombocom/rack-timeout) from 0.6.0 to 0.6.3.
- [Changelog](https://github.com/zombocom/rack-timeout/blob/main/CHANGELOG.md)
- [Commits](zombocom/rack-timeout@v0.6.0...v0.6.3)

---
updated-dependencies:
- dependency-name: rack-timeout
  dependency-type: direct:production
  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>

backend/Gemfile.lock

@@ -329,7 +329,7 @@ GEM
       rack (>= 2.0.0)
     rack-test (2.1.0)
       rack (>= 1.3)
-    rack-timeout (0.6.0)
+    rack-timeout (0.6.3)
     rails (6.1.7.6)
       actioncable (= 6.1.7.6)
       actionmailbox (= 6.1.7.6)