Update quick-xml requirement from 0.20 to 0.21

Updates the requirements on [quick-xml](https://github.com/tafia/quick-xml) to permit the latest version.
- [Release notes](https://github.com/tafia/quick-xml/releases)
- [Changelog](https://github.com/tafia/quick-xml/blob/master/Changelog.md)
- [Commits](https://github.com/tafia/quick-xml/compare/v0.20.0...v0.21.0)

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

lib/Cargo.toml

@@ -24,7 +24,7 @@ http_client = ["httparse", "native-tls"]
 [dependencies]
 rocksdb = { version = "0.15", optional = true }
 sled = { version = "0.34", optional = true }
-quick-xml = "0.20"
+quick-xml = "0.21"
 rand = "0.8"
 md-5 = "0.9"
 sha-1 = "0.9"