Update underscore to 1.13.8.

[desrosj]

Trac ticket: Core-64891.

Use of AI Tools

No AI usage.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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Core Committers: Use this line as a base for the props when committing in SVN:

Props desrosj, jonsurrell.

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[github-actions]

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[sirreal]

Thanks, I think it's a good idea to get this into 7.0.

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 62060
GitHub commit: b790d2f

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.