deps: update reqwest requirement from 0.12 to 0.13 in /backend

Updates the requirements on [reqwest](https://github.com/seanmonstar/reqwest) to permit the latest version.
- [Release notes](https://github.com/seanmonstar/reqwest/releases)
- [Changelog](https://github.com/seanmonstar/reqwest/blob/master/CHANGELOG.md)
- [Commits](seanmonstar/reqwest@v0.12.0...v0.13.1)

---
updated-dependencies:
- dependency-name: reqwest
  dependency-version: 0.13.1
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/Cargo.toml

@@ -43,7 +43,7 @@ time = "0.3"
 sha2 = "0.10"
 hmac = "0.12"
 subtle = "2.5"
-reqwest = { version = "0.12", features = ["json"] }
+reqwest = { version = "0.13", features = ["json"] }
 html-escape = "0.2"
 rand = "0.8"