Bump actions/upload-artifact from 5 to 6 in /.github/workflows

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

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

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -44,7 +44,7 @@ jobs:
       - name: Generate
         run: cargo r -p api_gen
       - name: Upload crate source
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: crate-source
           path: sys/src/**/*bindings.rs