Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -64,7 +64,7 @@ jobs:
 
         steps:
             -   name: Download docs artifact
-                uses: actions/download-artifact@v5
+                uses: actions/download-artifact@v6
                 with:
                     name: docs
                     path: artifacts
@@ -109,12 +109,12 @@ jobs:
 
         steps:
             -   name: Download docs artifact
-                uses: actions/download-artifact@v5
+                uses: actions/download-artifact@v6
                 with:
                     name: docs
 
             -   name: Download robots artifact
-                uses: actions/download-artifact@v5
+                uses: actions/download-artifact@v6
                 with:
                     name: robots
 
@@ -152,7 +152,7 @@ jobs:
 
         steps:
             -   name: Download search artifact
-                uses: actions/download-artifact@v5
+                uses: actions/download-artifact@v6
                 with:
                     name: ${{ env.ARTIFACT_INDEXES }}