CI: Add build-module to unit test assets

[sirreal]

What?

build-module was not included in the built unit test assets which can cause test failures.

This was overlooked in #65064.

This is a fix extracted from #65460.

Why?

The compiled assets are cached and shared across unit tests. This applies to both build and build-module directories.

Testing Instructions

CI passes. Also review CI on #65460.

[github-actions]

Flaky tests detected in a9a3825.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/10948606263
📝 Reported issues:

• [Flaky Test] Should insert content using the global inserter #57525 in /test/e2e/specs/widgets/editing-widgets.spec.js

[sirreal]

Why do I see these test failures here?

19) WP_Block_Supports_Colors_Test::test_gradient_with_individual_skipped_serialization_block_supports
Error: Call to undefined function gutenberg_style_engine_get_styles()

[sirreal]

Ok, this has fixed things. You can see PHP tests passing in #65460 now (with this merged).

[github-actions]

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[sirreal]

I've aded the backport label. This won't affect the plugin at all but it could cause problems on CI on branches if this is not fixed.

[sirreal]

Here we need to list all the paths.

If multiple paths are provided as input, the least common ancestor of all the search paths will be used as the root directory of the artifact. Exclude paths do not affect the directory structure.

[sirreal]

Here we remove the path so that it extracts all the assets correctly instead of naming them.

Before, since there was one directory in the aftifact, naming it build was OK. Now that we have a parent directory with build and build-module it just goes into the working directory.

[gziolo]

Tested with the linked PR and the changes make sense 👍🏻