fix(ci): pin Node via setup-node in bump-gitstream-core workflow [skip ci] - #532

describe-changes@v1: with concatenate mode: append

✨ PR Description

Purpose: Pin Node.js version in bump-gitstream-core workflow using setup-node action to ensure consistent build environment.

Main changes:

• Added setup-node action with node-version-file pointing to .nvmrc for reproducible Node version management

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