Adjust GitHub Actions so linting occurs separately from test suite

What?
=====

This adjusts the GitHub Actions setup so running `standard`
occurs separately from running the specs via Appraisal.

.github/workflows/build.yml

@@ -68,4 +68,17 @@ jobs:
       - name: Setup project
         run: bundle install
       - name: Run test
-        run: bundle exec rake
+        run: bundle exec rake all_specs
+
+  standard:
+    name: Run standard
+    runs-on: 'ubuntu-latest'
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "3.1"
+      - name: Setup project
+        run: bundle install
+      - name: Run test
+        run: bundle exec rake standard

Rakefile

@@ -8,8 +8,11 @@ require "standard/rake"
 
 Bundler::GemHelper.install_tasks(name: "factory_bot")
 
-desc "Default: run the specs, features, and standard ."
-task default: %w[spec:unit spec:acceptance features standard]
+desc "Default: run all specs and standard"
+task default: %w[all_specs standard]
+
+desc "Run all specs and features"
+task all_specs: %w[spec:unit spec:acceptance features]
 
 namespace :spec do
   desc "Run unit specs"