fix js oom `js-scripts` (#6139)
Fix `oom` failures (`FATAL ERROR: Ineffective mark-compacts near heap
limit Allocation failed - JavaScript heap out of memory`), like:
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7602589
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7602594
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Co-authored-by: Bastian Köcher <[email protected]>