CI: Update to Ruby 4.0

Signed-off-by: Tim Meusel <tim@bastelfreak.de>

Author: bastelfreak

.github/workflows/main.yml

@@ -32,7 +32,7 @@ jobs:
 
 
         os: [ubuntu-24.04]
-        ruby: ['3.4']
+        ruby: ['4.0']
 
         # Defaults for special-case influencing vars
         lein-profile: ['']
@@ -43,17 +43,17 @@ jobs:
           # lint
           - flavor: lint/openjdk21
             os: ubuntu-24.04
-            ruby: '3.4'
+            ruby: '4.0'
 
           # unit
           # jdk 25
           - flavor: core+ext/openjdk25/pg-18
             os: ubuntu-24.04
-            ruby: '3.4'
+            ruby: '4.0'
           # jdk 21
           - flavor: core+ext/openjdk21/pg-18
             os: ubuntu-24.04
-            ruby: '3.4'
+            ruby: '4.0'
 
     steps:
       - name: Compute job outputs
@@ -188,7 +188,7 @@ jobs:
       - name: setup ruby
         uses: ruby/setup-ruby@9eb537ca036ebaed86729dcb9309076e4c5c3b74 # v1.314.0
         with:
-          ruby-version: '3.2'
+          ruby-version: '4.0'
           bundler-cache: true
       - name: Run RSpec
         run: bundle exec rspec spec -fd