Bump actions/upload-artifact from 5 to 6 (#520)

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/ci.yml

@@ -67,13 +67,13 @@ jobs:
         ls -al dist/ # Verify the wheel is created
 
     - name: Upload Wheel Artifact
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: mcpartools-wheel
         path: dist/*.whl
 
     - name: Upload Sample Test Data Artifact
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: sample-fluka-input
         path: tests/res/sample_fluka.inp
@@ -152,7 +152,7 @@ jobs:
 
       - name: Upload Zipapp Executable as Artifact
         # This step makes the .pyz file available if needed for later stages (e.g., release)
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: generatemc-zipapp
           path: generatemc.pyz

.github/workflows/release.yml

@@ -49,17 +49,17 @@ jobs:
         pyinstaller main.spec
         ls -al dist/generatemc
 
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       with:
         name: single
         path: dist/generatemc
 
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       with:
         name: wheel
         path: dist/*.whl
 
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       with:
         name: source
         path: dist/*.tar.gz