add mkdir command for coverage directory

Author: AlaaElattar

melos.yaml

@@ -13,6 +13,7 @@ scripts:
     description: Merge all packages coverage trace files ignoring data related to generated files.
     run: |
       melos exec rm -rf coverage
+      mkdir -p coverage # Ensure the coverage directory exists
       melos run unit_test
       melos exec -c 1 --file-exists=coverage/lcov.info -- coverde filter --input ./coverage/lcov.info --output MELOS_ROOT_PATH/coverage/filtered.lcov.info --filters \.g\.dart
       coverde value -i coverage/filtered.lcov.info > MELOS_ROOT_PATH/coverage/result.txt