Test on Ruby 2.7 and 3.2

Use current latest stable release of Ruby for tests.

Ruby 2.7 reached end of life on 2023-03-31. We still test on the older
version for completeness, as Middleman v4 plans to keep support for Ruby
2.7 indefinitely [[1]].

[1]: middleman/middleman#2614 (comment)

Author: lfdebrux

.github/workflows/test.yaml

@@ -7,6 +7,10 @@ jobs:
     name: Test
     runs-on: ubuntu-latest
 
+    strategy:
+      matrix:
+        ruby: ['2.7', '3.2']
+
     steps:
       - uses: actions/checkout@v2
 
@@ -17,6 +21,7 @@ jobs:
 
       - uses: ruby/setup-ruby@v1
         with:
+          ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
 
       - name: Run tests

.rubocop.yml

@@ -2,6 +2,9 @@ inherit_gem:
   rubocop-govuk:
     - config/default.yml
 
+AllCops:
+  TargetRubyVersion: 2.7
+
 Layout/HeredocIndentation:
   Enabled: false