Don't include steep in the dev-deps

instead, put it in the Gemfile, and allow an ENV to exclude it, which we
can then supply in the rspec github actions. We need to run tests in
environments that steep doesn't support, and gemspecs don't (as yet)
support optional dev dependencies.

.github/workflows/rspec.yml

@@ -9,6 +9,8 @@ jobs:
       fail-fast: false
       matrix:
         ruby-version: ['2.7', '3.0', '3.1', '3.2', 'head']
+    env:
+      NO_STEEP: "Because we need to test on versions that are older than steep supports"
 
     steps:
       - uses: actions/checkout@v3

Gemfile

@@ -1,3 +1,7 @@
 source "https://rubygems.org"
 
 gemspec
+
+unless ENV["NO_STEEP"]
+  gem "steep", "~> 1.6.0"
+end

environment_helpers.gemspec

@@ -36,5 +36,4 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rubocop", "~> 1.50"
   spec.add_development_dependency "quiet_quality", "~> 1.3.0"
   spec.add_development_dependency "mdl", "~> 0.12"
-  spec.add_development_dependency "steep", "~> 1.6.0"
 end