describe-changes@v1: with concatenate mode: append

✨ PR Description

Purpose: Update @linearb/gitstream-core dependency to version 2.1.267 and add isolated-vm as external package in build configuration.

Main changes:

• Bumped @linearb/gitstream-core from version 2.1.264 to 2.1.267 to incorporate latest fixes and features
• Added isolated-vm to external packages list in ncc build script to prevent bundling

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