Track the latest Ruby 4.x alongside the pinned 4.0.5

Evergreen is on 4.0.5 today, so keep that exact version covered, and add a
'4' entry that setup-ruby resolves to the newest 4.x it knows about.

Author: grantcox

.github/workflows/ci.yml

@@ -10,7 +10,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', '3.4', '4.0.5', 'jruby-9.3']
+        # '4' is a prefix match resolved against the version list baked into the
+        # setup-ruby commit pinned below, so it only tracks new 4.x releases as far
+        # as that pin. Bump the pin to pick up newer ones.
+        ruby: ['2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', '3.4', '4.0.5', '4', 'jruby-9.3']
     steps:
       - uses: actions/checkout@a37ce9120846195fa4ece8f58b268e6043cb2f26 # v3
       - name: Setup ruby