Bump dawidd6/action-download-artifact from 2 to 6 in /.github/workflows (#2629)

Bumps [dawidd6/action-download-artifact](https://github.com/dawidd6/action-download-artifact) from 2 to 6.
- [Release notes](https://github.com/dawidd6/action-download-artifact/releases)
- [Commits](dawidd6/action-download-artifact@v2...v6)

---
updated-dependencies:
- dependency-name: dawidd6/action-download-artifact
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/build-linux.yml

@@ -91,7 +91,7 @@ jobs:
           key: test-extra-code
 
       - name: Fetch main build of ocamlformat
-        uses: dawidd6/action-download-artifact@v2
+        uses: dawidd6/action-download-artifact@v6
         with:
           workflow: build-linux.yml
           workflow_conclusion: ""