Update actions/checkout action to v6 (#29)

Co-authored-by: elastic-renovate-prod[bot] <174716857+elastic-renovate-prod[bot]@users.noreply.github.com>

Author: elastic-renovate-prod[bot]

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
   checks:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
       - uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5
         with:
           distribution: 'temurin'