bump extension artifact to v4

Author: ccfelius

.github/workflows/_extension_deploy.yml

@@ -92,7 +92,7 @@ jobs:
           cd duckdb
           git checkout ${{ inputs.duckdb_version }}
 
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v4
         with:
           name: ${{ inputs.extension_name }}-${{ inputs.duckdb_version }}-extension-${{matrix.duckdb_arch}}${{inputs.artifact_postfix}}${{startsWith(matrix.duckdb, 'wasm') && '.wasm' || ''}}
           path: |