stellar-core 28.0.0

[BrewTestBot]

Created by brew bump

---

Created with brew bump-formula-pr.

[botantony]

     Compiling ethnum v1.5.0
  error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
    --> /Users/brew/Library/Caches/Homebrew/cargo_cache/registry/src/index.crates.io-1949cf8c6b5b557f/ethnum-1.5.0/src/error.rs:16:14
     |
  16 |     unsafe { mem::transmute(()) }
     |              ^^^^^^^^^^^^^^
     |
     = note: source type: `()` (0 bits)
     = note: target type: `TryFromIntError` (8 bits)

This was fixed in nlordell/ethnum-rs#58 (ethnum 1.5.3) but some submodules use old crate version