ci: 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] <[email protected]>

Author: dependabot[bot]

.github/workflows/release.yml

@@ -99,7 +99,7 @@ jobs:
         run: cat RELEASE_NOTES.md
 
       - name: Upload release notes as artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: release-notes
           path: RELEASE_NOTES.md

.github/workflows/wasm.yml

@@ -141,7 +141,7 @@ jobs:
           echo "✓ TypeScript definitions valid"
 
       - name: Upload WASM build artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: wasm-build-${{ matrix.target }}
           path: crates/pjs-wasm/pkg-${{ matrix.target }}/
@@ -191,7 +191,7 @@ jobs:
           cat bundle-report.md
 
       - name: Upload bundle size report
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: bundle-size-report
           path: bundle-report.md
@@ -318,7 +318,7 @@ jobs:
           echo "✓ Test package created"
 
       - name: Upload validated package
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: validated-wasm-package
           path: wasm-pkg/