Update secp256k1 requirement from 0.24.3 to 0.28.0

Updates the requirements on [secp256k1](https://github.com/rust-bitcoin/rust-secp256k1) to permit the latest version.
- [Changelog](https://github.com/rust-bitcoin/rust-secp256k1/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-bitcoin/rust-secp256k1/commits/secp256k1-0.28.0)

---
updated-dependencies:
- dependency-name: secp256k1
  dependency-type: direct:production
...

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

honey-badger/Cargo.toml

@@ -8,7 +8,7 @@ base64 = "0.21.0"
 bdk = { version = "0.28.0", features = ["keys-bip39"] }
 log = "0.4.17"
 rand = "0.8.5"
-secp256k1 = { version = "0.24.3", features = ["global-context"] }
+secp256k1 = { version = "0.28.0", features = ["global-context"] }
 serde_json = "1.0"
 
 graphql = { path = "../graphql" }