Add release:latest_github_release task

Requires installing the `gh` CLI. Gets the latest release from GitHub and outputs the version to STDOUT.

tasks/release.rake

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require "rake"
+
+desc "Gets the latest GitHub release version, e.g: v1.1.1"
+task "release:latest_github_release" do
+  # We could use `git` here to get the most recent version tag, like:
+  #   `git tag --list --sort='-version:refname' 'v*' | head -n1`
+  # but we go through the `gh` because we want the latest _GitHub_ release.
+  $stdout << `gh release view --json tagName --jq '.tagName'`
+end