Update bitcoincore-rpc requirement from 0.14 to 0.15

Updates the requirements on [bitcoincore-rpc](https://github.com/rust-bitcoin/rust-bitcoincore-rpc) to permit the latest version.
- [Release notes](https://github.com/rust-bitcoin/rust-bitcoincore-rpc/releases)
- [Changelog](https://github.com/rust-bitcoin/rust-bitcoincore-rpc/blob/master/CHANGELOG.md)
- [Commits](rust-bitcoin/rust-bitcoincore-rpc@v0.14.0...v0.15.0)

---
updated-dependencies:
- dependency-name: bitcoincore-rpc
  dependency-type: direct:production
...

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

testcontainers/Cargo.toml

@@ -28,7 +28,7 @@ tokio = { version = "1", features = [ "macros" ], optional = true }
 experimental = [ "async-trait", "bollard", "tokio" ]
 
 [dev-dependencies]
-bitcoincore-rpc = "0.14"
+bitcoincore-rpc = "0.15"
 json = "0.12"
 lapin = "1.8.0"
 mongodb = "2.1.0"