Bump actions/upload-artifact from 5 to 6

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/build-assets.yml

@@ -59,7 +59,7 @@ jobs:
         uses: actions/attest-build-provenance@v3
         with:
           subject-path: '${{ github.workspace }}/pie.phar'
-      - uses: actions/upload-artifact@v5
+      - uses: actions/upload-artifact@v6
         with:
           name: pie-${{ github.sha }}.phar
           path: pie.phar
@@ -155,7 +155,7 @@ jobs:
         with:
           subject-path: '${{ github.workspace }}/${{ env.PIE_BINARY_OUTPUT }}'
 
-      - uses: actions/upload-artifact@v5
+      - uses: actions/upload-artifact@v6
         with:
           name: pie-${{ github.sha }}-${{ runner.os }}-${{ runner.arch }}.bin
           path: ${{ env.PIE_BINARY_OUTPUT }}