Set prefer-dedupe true in npm configuration

This change was applied in Gutenberg:

WordPress/gutenberg#61630

Quoting that :

> The `npm dedupe` command searches
> and attempts to simplify the overall structure of the local package
> tree to allow dependent packages to be shared more effectively. As
> detailed in #61532, reducing the amount of dependency duplication is
> beneficial for a few reasons:
>
> - Fewer packages overall.
> - Faster installation.
> - Less size to transfer and store on disk.
> - Usually bundle size is reduced (although this depends on which
>   versions of packages are used).
>
> However, unless the command is run regularly, the project's dependency
> tree easily falls out of order.

See https://docs.npmjs.com/cli/v10/commands/npm-dedupe

.npmrc

@@ -1,3 +1,4 @@
 save-exact = true
 engine-strict = true
 legacy-peer-deps = true
+prefer-dedupe = true