⬆️ Bump actions/upload-artifact from 5 to 6 (#675)

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

Author: dependabot[bot]

.github/workflows/cache.yml

@@ -40,13 +40,13 @@ jobs:
         run: |
           jb build lectures --path-output ./ -W --keep-going
       - name: Upload Execution Reports (HTML)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: execution-reports
           path: _build/html/reports
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: build-cache
           path: _build

.github/workflows/ci.yml

@@ -52,7 +52,7 @@ jobs:
           mkdir -p _build/html/_pdf
           cp -u _build/latex/*.pdf _build/html/_pdf
       - name: Upload Execution Reports (LaTeX)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: execution-reports
@@ -72,7 +72,7 @@ jobs:
           rm -r _build/.doctrees
           jb build lectures --path-output ./ -nW --keep-going
       - name: Upload Execution Reports (HTML)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: execution-reports

.github/workflows/collab.yml

@@ -37,7 +37,7 @@ jobs:
         run: |
           jb build lectures --path-output ./ -n -W --keep-going
       - name: Upload Execution Reports
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: execution-reports

.github/workflows/publish.yml

@@ -115,7 +115,7 @@ jobs:
           publish_dir: _build/html/
           cname: intro.quantecon.org
       - name: Upload "_build" folder (cache)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: build-publish
           path: _build