Make default Rails version 7.X instead of 7.0.X (#85)

* Make default Rails version 7.X instead of 7.0.X

When trying to launch the Rails server with the Rails version set to the
latest 7.0.X, it fails with the following error message:

```txt
uninitialized constant ActiveSupport::LoggerThreadSafeLevel::Logger (NameError)
```

The [issue](rails/rails#54271) has been solved in
Rails version 7.1.X, and so we should stop using the 7.0.X version as the
default in development mode for the showcase engine.

* Run bin/highlights to make test pass

* Drop support for Rails 6.X and Ruby 2.X

Author: alexandreruban

.github/workflows/ci.yml

@@ -13,12 +13,11 @@ jobs:
       fail-fast: false
       matrix:
         rails-version:
-          - "7.1"
-          - "6.1"
+          - "7.2"
+          - "8.0"
           - "main"
         ruby-version:
-          - "3.2"
-          - "2.7"
+          - "3.4"
 
     env:
       RAILS_ENV: test

Gemfile

@@ -6,7 +6,7 @@ gemspec
 
 gem "sqlite3"
 
-rails_version = ENV.fetch("RAILS_VERSION", "7.0")
+rails_version = ENV.fetch("RAILS_VERSION", "7")
 
 rails_constraint = if rails_version == "main"
   {github: "rails/rails"}

app/assets/builds/showcase.highlights.css

@@ -39,6 +39,10 @@
   color: #116329;
   background-color: #dafbe1;
 }
+.sc-highlight .ges {
+  font-weight: bold;
+  font-style: italic;
+}
 .sc-highlight .kc {
   color: #0550ae;
 }
@@ -153,6 +157,10 @@
     color: #aff5b4;
     background-color: #033a16;
   }
+  .sc-highlight .ges {
+    font-weight: bold;
+    font-style: italic;
+  }
   .sc-highlight .kc {
     color: #79c0ff;
   }

showcase.gemspec

@@ -17,6 +17,6 @@ Gem::Specification.new do |spec|
     Dir["{app,config,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
   end
 
-  spec.add_dependency "rails", ">= 6.1.0"
+  spec.add_dependency "rails", ">= 7.2"
   spec.add_development_dependency "tailwindcss-rails"
 end