Updated checkout action [skip ci]

Author: ankane

.github/workflows/build.yml

@@ -4,7 +4,7 @@ jobs:
   build:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: ankane/setup-postgres@v1
         with:
           database: pgvector_cpp_test