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/ci.yml

@@ -26,7 +26,7 @@ jobs:
       - name: Linux build
         run: processing-java --sketch=./MusicBeam --output=./output --force --export
       - name: Upload Linux Build
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Linux Build
           path: output
@@ -50,7 +50,7 @@ jobs:
       - name: Windows build
         run: processing-java --sketch=./MusicBeam --output=./output --variant=windows-amd64 --force --export
       - name: Upload Windows Build
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Windows Build
           path: output