build(deps): update minicbor requirement from 0.19 to 0.21

Updates the requirements on [minicbor](https://gitlab.com/twittner/minicbor) to permit the latest version.
- [Changelog](https://gitlab.com/twittner/minicbor/blob/develop/CHANGELOG.md)
- [Commits](https://gitlab.com/twittner/minicbor/compare/minicbor-v0.19.0...minicbor-v0.21.0)

---
updated-dependencies:
- dependency-name: minicbor
  dependency-type: direct:production
...

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

Cargo.toml

@@ -13,7 +13,7 @@ repository = "https://github.com/dspicher/ur-rs/"
 [dependencies]
 bitcoin_hashes = { version = "0.12", default-features = false }
 crc = "3"
-minicbor = { version = "0.19", features = ["alloc"] }
+minicbor = { version = "0.21", features = ["alloc"] }
 phf = { version = "0.11", features = ["macros"], default-features = false }
 rand_xoshiro = "0.6"