chore(deps): bump the github-actions group with 2 updates (#162)

Bumps the github-actions group with 2 updates: [actions/upload-artifact](https://github.com/actions/upload-artifact) and [actions/download-artifact](https://github.com/actions/download-artifact).


Updates `actions/upload-artifact` from 6 to 7
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v6...v7)

Updates `actions/download-artifact` from 7 to 8
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v7...v8)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: github-actions
- dependency-name: actions/download-artifact
  dependency-version: '8'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: github-actions
...

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/test.yaml

@@ -131,7 +131,7 @@ jobs:
 
     - name: Upload artifacts
       if: always()
-      uses: actions/upload-artifact@v6
+      uses: actions/upload-artifact@v7
       with:
         name: results-${{ matrix.os }}
         path: |

.github/workflows/update-lockfile.yaml

@@ -38,7 +38,7 @@ jobs:
         pixi workspace export conda-environment -e default envs/environment.yaml -n pypsa-eur
 
     - name: Upload artifacts
-      uses: actions/upload-artifact@v6
+      uses: actions/upload-artifact@v7
       with:
         name: lockfiles
         path: |
@@ -51,7 +51,7 @@ jobs:
     steps:
     - uses: actions/checkout@v6
     - name: Download all artifacts
-      uses: actions/download-artifact@v7
+      uses: actions/download-artifact@v8
       with:
         name: lockfiles