ci: Update to upload-artifact@v7 and download-artifact@v8

Author: dependabot[bot]

.github/workflows/export.yml

@@ -27,7 +27,7 @@ jobs:
           godot_version: "4.6"
 
       - name: Upload web artifact
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
           name: web
           path: build/web
@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download web bundle
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         with:
           name: web
           path: web