Bump bitcoin from 0.32.7 to 0.32.8 in /backend (#163)

Bumps [bitcoin](https://github.com/rust-bitcoin/rust-bitcoin) from 0.32.7 to 0.32.8.
- [Release notes](https://github.com/rust-bitcoin/rust-bitcoin/releases)
- [Changelog](https://github.com/rust-bitcoin/rust-bitcoin/blob/master/CHANGELOG.md)
- [Commits](rust-bitcoin/rust-bitcoin@bitcoin-0.32.7...bitcoin-0.32.8)

---
updated-dependencies:
- dependency-name: bitcoin
  dependency-version: 0.32.8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

backend/Cargo.lock

@@ -5,7 +5,7 @@
 
 [dependencies]
   axum = { version = "0.8" }
-  bitcoin = { version = "0.32.5", features = [ "serde" ] }
+  bitcoin = { version = "0.32.8", features = [ "serde" ] }
   chrono = { version = "0.4.38", features = ["serde"] }
   clap = { version = "4.5", features = [ "derive" ] }
   hex = { version = "0.4" }