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.yml

@@ -36,7 +36,7 @@ jobs:
         run: castle-engine package --os=win64 --cpu=x86_64 --verbose
       - name: Archive Artifacts
         # See https://github.com/actions/upload-artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: windows-build
           # Note: Keep paths that start with asterisk in double qoutes, to avoid misinterpreting as YAML reference.
@@ -48,7 +48,7 @@ jobs:
       - name: Package Linux
         run: castle-engine package --os=linux --cpu=x86_64 --verbose
       - name: Archive Artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: linux-build
           path: "*-linux-x86_64.tar.gz"