bump Ruby 3.3.8 on CI

Author: suketa

.github/workflows/test_on_macos.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: macos-latest
     strategy:
       matrix:
-        ruby: ['3.1.6', '3.2.7', '3.3.7', '3.4.2', 'head']
+        ruby: ['3.1.6', '3.2.7', '3.3.8', '3.4.2', 'head']
         duckdb: ['1.2.1', '1.1.3', '1.1.1']
 
     steps:

.github/workflows/test_on_ubuntu.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ['3.1.6', '3.2.7', '3.3.7', '3.4.2', 'head']
+        ruby: ['3.1.6', '3.2.7', '3.3.8', '3.4.2', 'head']
         duckdb: ['1.2.1', '1.1.3', '1.1.1']
 
     steps: