Add user locale in the parameters of the get_tasks endpoint

[leonidasmi]

Context

Summary

This PR can be summarized in the following changelog entry:

• Fixes a bug where the task list copies would be displayed in the site language instead of the user language.

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

1. Install and activate Yoast SEO
2. Set the site language to English
3. Set the user language to other language, e.g. dutch (Note, the language you pick might not have the translations ready for what we're about to test, so pick a language with high percentage of translated strings, eg. Dutch)
4. Go to Yoast SEO > General > Task list
5. Confirm that the task title for creating llms.txt file/removing the hello world post/create new content tasks are in the user language and not in the site language (new tasks titles are not translated yet, so we have to check the old tasks)
6. Open the task modal of one of those tasks

Without this PR

1. The task title is still rendered in site language (English)
2. Open the task modal
3. The task title and call to action sections inside the modal are all rendered in site language (English)

With this PR

1. The task title is rendered in user language (dutch)
2. Open the task modal
3. The task title and call to action sections inside the modal are all rendered in user language (dutch)

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

• Smoke test the task list in other languages (like have a user have the site default as their language)
  • Confirm that completing tasks work too (check with the Enable llms.txt at least)

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.
• This PR also affects Yoast SEO for Google Docs. I have added a changelog entry starting with [yoast-doc-extension], added test instructions for Yoast SEO for Google Docs and attached the Google Docs Add-on label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.
• I have run grunt build:images and commited the results, if my PR introduces new images or SVGs.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #

[vraja-pro]

Test with the titles, about text is not yet translated.

CR & AC ✅