Build/Test Tools: Remove npx commands in 7.0

[adimoldovan]

Backport of r63309, already in trunk via #13021, to the 7.0 branch. It replaces the last two npx calls in Gruntfile.js with npm exec --no, which runs an installed binary instead of downloading and installing one, and declares update-browserslist-db as a direct devDependency.

Trac ticket: https://core.trac.wordpress.org/ticket/65864

Testing instructions

1. Run npm ci. It completes, and git status stays clean. This confirms package.json and package-lock.json agree.
2. Run npm ls update-browserslist-db. It reports update-browserslist-db@1.2.3 as a direct dependency.
3. Run npm exec --no -- update-browserslist-db --help and npm exec --no -- wp-scripts. Each runs the local binary and downloads nothing.
4. Delete node_modules/update-browserslist-db and run npm exec --no -- update-browserslist-db. It fails with npx canceled due to missing packages and no YES option instead of fetching the package. Restore the tree with npm ci.

Use of AI Tools

AI assistance: Yes — Claude Code (Claude Opus 5) applied r63309 to the 7.0 branch and verified the changeset.

---

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]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

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

Props adrianmoldovanwp.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.