⬆️ Bump actions/upload-artifact from 2 to 4 (#254)

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 2 to 4.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v2...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/cache.yml

@@ -26,7 +26,7 @@ jobs:
         run: |
           jb build lectures --path-output ./
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: build-cache
           path: _build

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
         run: |
           jb build lectures --path-output ./ -W --keep-going
       - name: Upload Execution Reports
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: failure()
         with:
           name: execution-reports

.github/workflows/publish.yml

@@ -40,7 +40,7 @@ jobs:
         run: |
           jb build lectures --path-output ./ --builder=custom --custom-builder=jupyter
           zip -r download-notebooks.zip _build/jupyter
-      - uses: actions/upload-artifact@v2
+      - uses: actions/upload-artifact@v4
         with:
           name: download-notebooks
           path: download-notebooks.zip
@@ -60,7 +60,7 @@ jobs:
         run: |
           jb build lectures --path-output ./ -W --keep-going
       - name: Upload Execution Reports
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: failure()
         with:
           name: execution-reports
@@ -72,7 +72,7 @@ jobs:
           publish_dir: _build/html/
           cname: datascience.quantecon.org
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: build-publish
           path: _build