Bump actions/download-artifact from 3 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 3 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v3...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/clingo.yml

@@ -132,7 +132,7 @@ jobs:
           repository: spack/spack
           path: spack
           ref: d36452cf4e70fa1da8b9db43921850872b82ced9
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v6
         with:
           name: clingo_binary_mirror
       - run: ./spack/bin/spack python ./generate_bootstrap_json.py clingo

.github/workflows/gnupg.yml

@@ -128,7 +128,7 @@ jobs:
           repository: spack/spack
           path: spack
           ref: d36452cf4e70fa1da8b9db43921850872b82ced9
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v6
         with:
           name: gnupg_binary_mirror
       - run: ./spack/bin/spack python ./generate_bootstrap_json.py gnupg

.github/workflows/patchelf.yml

@@ -88,7 +88,7 @@ jobs:
           repository: spack/spack
           path: spack
           ref: d36452cf4e70fa1da8b9db43921850872b82ced9
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v6
         with:
           name: patchelf_binary_mirror
       - run: ./spack/bin/spack python ./generate_bootstrap_json.py patchelf