ci: bump actions/download-artifact from 5.0.0 to 6.0.0

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@634f93c...018cc2c)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -53,7 +53,7 @@ jobs:
           - { arch: aarch64, os: ubuntu-24.04-arm, wheel_tag: manylinux_aarch64 }
     steps:
       - name: Download source distribution
-        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
         with:
           name: source
       - name: Unpack source distribution
@@ -127,7 +127,7 @@ jobs:
       id-token: write
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-      - uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
+      - uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
         with:
           name: results
       - name: Upload test coverage to Codecov
@@ -157,7 +157,7 @@ jobs:
     # Upload to PyPI on every tag starting with 'v'
     if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags/v')
     steps:
-      - uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
+      - uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
         with:
           path: artifacts
       - run: |