chore(deps): bump actions/upload-artifact from 6 to 7

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 6 to 7.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v6...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/release.yml

@@ -54,17 +54,17 @@ jobs:
       - run: just doc handbooks
 
       - name: Upload bithesis.pdf for later usage.
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
           name: bithesis
           path: src/bithesis.pdf
       - name: Upload handbooks for later usage.
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
           name: handbooks
           path: "handbook/*.pdf"
       - name: Upload *.cls for later usage.
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
           name: cls
           path: "src/*.cls"
@@ -258,7 +258,7 @@ jobs:
           name: handbooks
           path: handbook
       - run: just pkg-only
-      - uses: actions/upload-artifact@v6
+      - uses: actions/upload-artifact@v7
         with:
           name: ctan-pkg
           path: target/bithesis.zip