Bump actions/upload-artifact from 4 to 7

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 7.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v7)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/plotters-core.yml

@@ -81,7 +81,7 @@ jobs:
           ../target/release/examples/$(basename ${example} .rs)
         done 
         tar -czvf example-outputs.tar.gz plotters-doc-data
-    - uses: actions/upload-artifact@v4
+    - uses: actions/upload-artifact@v7
       with:
           name: example-outputs
           path: plotters/example-outputs.tar.gz