Bump actions/checkout from v4 to v6

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

.github/workflows/rubocop.yml

@@ -16,7 +16,7 @@ jobs:
       LD_LIBRARY_PATH: /opt/oracle/instantclient_23_26
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up Ruby 4.0
       uses: ruby/setup-ruby@v1
       with:

.github/workflows/test.yml

@@ -50,7 +50,7 @@ jobs:
           --health-retries 10
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:

.github/workflows/test_11g.yml

@@ -50,7 +50,7 @@ jobs:
           --health-retries 10
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with: