chore(deps): bump ra from 2.17.2 to 3.1.5 (#2)

Bumps [ra](https://github.com/rabbitmq/ra) from 2.17.2 to 3.1.5.
- [Release notes](https://github.com/rabbitmq/ra/releases)
- [Commits](rabbitmq/ra@v2.17.2...v3.1.5)

---
updated-dependencies:
- dependency-name: ra
  dependency-version: 3.1.5
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

mix.exs

@@ -35,7 +35,7 @@ defmodule Phronesis.MixProject do
       {:jason, "~> 1.4"},
 
       # Raft consensus library for distributed consensus
-      {:ra, "~> 2.7"},
+      {:ra, "~> 3.1"},
 
       # Property-based testing with StreamData (CRG Grade C requirement)
       {:stream_data, "~> 1.0", only: :test}