Add RSpectre to CI

- This can help detect unused test setup on an ongoing basis and also helps me by giving me a bigger corpus of [`rspectre`](https://github.com/dgollahon/rspectre) users.

.github/workflows/ci.yml

@@ -149,3 +149,19 @@ jobs:
         ruby-version: ${{ matrix.ruby }}
         bundler-cache: true
     - run: bundle exec rubocop
+  rspectre:
+    name: RSpectre
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 10
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby: [ruby-3.2]
+        os: [ubuntu-latest]
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - run: bundle exec rspectre

Gemfile.lock

@@ -20,7 +20,7 @@ GEM
     diff-lcs (1.5.0)
     json (2.6.3)
     parallel (1.22.1)
-    parser (3.2.2.0)
+    parser (3.2.2.1)
       ast (~> 2.4.1)
     rainbow (3.1.1)
     regexp_parser (2.6.2)
@@ -41,6 +41,9 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.12.0)
     rspec-support (3.12.0)
+    rspectre (0.1.0)
+      parser (>= 3.2.2.1)
+      rspec (~> 3.9)
     rubocop (1.47.0)
       json (~> 2.3)
       parallel (~> 1.10)
@@ -70,6 +73,7 @@ DEPENDENCIES
   rspec (~> 3.10)
   rspec-core (~> 3.10)
   rspec-its (~> 1.3.0)
+  rspectre (~> 0.1)
   rubocop (~> 1.7)
 
 BUNDLED WITH

mutant.gemspec

@@ -34,5 +34,6 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency('rspec',      '~> 3.10')
   gem.add_development_dependency('rspec-core', '~> 3.10')
   gem.add_development_dependency('rspec-its',  '~> 1.3.0')
+  gem.add_development_dependency('rspectre',   '~> 0.1')
   gem.add_development_dependency('rubocop',    '~> 1.7')
 end