Credential Form: Show error message on the correct language + cleanup

[gabrielcaires]

Fix #95625 and continue the work started on Remove English-based verifications #95552

Proposed Changes

• Remove all locale checking from the credential step
• Add _locale flag to the ticket creation request

Context

This comment highlighted we are not showing an error message on the user language. I initially thought the reason was the missing _locale flag, but actually, I found another English checking that was making the UI show errors directly from the backend.

Now, the UI is showing correct error messages.

Testing Instructions

• Select any locale (excluding en) in your WordPress account
• Access any of the migration flows
• Go to the Do it for me
• Follow all steps until you reach the credential form
• Set a valid WordPress site
• Set invalids credentials
• Check if the error messages are using the correct language.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122722

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https://calypso.live?image=registry.a8c.com/calypso/app:build-122722&env=jetpack

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https://calypso.live?image=registry.a8c.com/calypso/app:build-122722&env=a8c-for-agencies

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/remove-english-checkings on your sandbox.

[sixhours]

Super nitpicky, but we should reverse this conditional so the constant is on the left-hand side ("Yoda" conditions as per WP coding standards)

[gabrielcaires]

Thanks @sixhours.
I just double-checked if we are adopting the WP pattern, and I saw we just have
164 instances of the Yoda style
1494 instances of the regular style.

I run a search using the following patterns:
Regular style

=== '

Yoda style

' === 

The javascript WordPress code standards also contain examples of "regular" style usage.
https://developer.wordpress.org/coding-standards/wordpress-coding-standards/javascript/

So, I think the Yoda style is more applicable to PHP

[sixhours]

Confirmed this fixes the error message translations!