chore(deps): update actions/download-artifact action to v8

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -117,11 +117,11 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ github.event_name == 'release' }}
     steps:
-      - uses: actions/download-artifact@v6
+      - uses: actions/download-artifact@v8
         with:
           name: ghostty-appimage-aarch64
 
-      - uses: actions/download-artifact@v6
+      - uses: actions/download-artifact@v8
         with:
           name: ghostty-appimage-x86_64
 
@@ -145,11 +145,11 @@ jobs:
       contents: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/download-artifact@v6
+      - uses: actions/download-artifact@v8
         with:
           name: ghostty-appimage-aarch64
 
-      - uses: actions/download-artifact@v6
+      - uses: actions/download-artifact@v8
         with:
           name: ghostty-appimage-x86_64