⬆️ Bump actions/upload-artifact from 2 to 4 (#489)

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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/cache.yml

@@ -39,13 +39,13 @@ jobs:
         run: |
           jb build lectures --path-output ./ -W --keep-going
       - name: Upload Execution Reports (HTML)
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: failure()
         with:
           name: execution-reports
           path: _build/html/reports
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: build-cache
           path: _build

.github/workflows/linkcheck.yml

@@ -37,7 +37,7 @@ jobs:
         shell: bash -l {0}
         run: jb build lectures --path-output=./ --builder=custom --custom-builder=linkcheck
       - name: Upload Link Checker Reports
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: failure()
         with:
           name: linkcheck-reports

.github/workflows/publish.yml

@@ -89,7 +89,7 @@ jobs:
           publish_dir: _build/html/
           cname: intro.quantecon.org
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: build-publish
           path: _build