Bump miniconf_mqtt from 0.16.2 to 0.18.0

Bumps [miniconf_mqtt](https://github.com/quartiq/miniconf) from 0.16.2 to 0.18.0.
- [Release notes](https://github.com/quartiq/miniconf/releases)
- [Changelog](https://github.com/quartiq/miniconf/blob/main/CHANGELOG.md)
- [Commits](quartiq/miniconf@v0.16.2...v0.18.0)

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

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

Cargo.toml

@@ -52,7 +52,7 @@ encdec = { version = "0.9", default-features = false }
 crc-any = { version = "2.5.0", default-features = false }
 panic-persist = { version = "0.3", features = ["custom-panic-handler", "utf8"] }
 miniconf = { version = "0.16", features = ["json-core", "derive", "postcard"]}
-miniconf_mqtt = "0.16"
+miniconf_mqtt = "0.18"
 # Note: Keep `py/pyproject.toml` version in sync with the Minimq version used in FW.
 minimq = "0.9.0"
 w5500 = "0.5"