ci: use ruby v4 (#657)

* ci: add ruby v4

* do not run 4 on win

* use 4 for func test

Author: KazuCocoa

.github/workflows/functional-test.yml

@@ -100,7 +100,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: 3.2
+        ruby-version: 4.0
     - name: Install dependencies
       run: bundle install
 

.github/workflows/unittest.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [3.1, 3.2, 3.3]
+        ruby: [3.1, 3.2, 3.3, 4.0]
 
     runs-on: ubuntu-latest
 
@@ -39,6 +39,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        # 4.0 is not available on Win env yet.
         ruby: [3.1, 3.2, 3.3]
 
     runs-on: windows-latest