Update to actions/checkout@v6

Author: jeremyevans

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
     env:
       BUNDLE_GEMFILE: .ci.gemfile
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - run: sudo apt-get -yqq install libpq-dev
     - uses: ruby/setup-ruby@v1
       with: