Bump tower-http from 0.5.2 to 0.6.6 in /backend (#60)

Bumps [tower-http](https://github.com/tower-rs/tower-http) from 0.5.2 to 0.6.6.
- [Release notes](https://github.com/tower-rs/tower-http/releases)
- [Commits](tower-rs/tower-http@tower-http-0.5.2...tower-http-0.6.6)

---
updated-dependencies:
- dependency-name: tower-http
  dependency-version: 0.6.6
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/Cargo.lock

@@ -18,7 +18,7 @@
     "raw_value",
   ] }
   tokio = { version = "1.44.2", features = [ "macros", "rt-multi-thread" ] }
-  tower-http = { version = "0.5", features = [ "cors" ] }
+  tower-http = { version = "0.6", features = [ "cors" ] }
   tracing = { version = "0.1" }
   tracing-subscriber = { version = "0.3.18", features = [ "env-filter" ] }