[Brand Updates] Update promo screenshots colors

[hichamboushaba]

Closes: woocommerce/woomobile-private#399

Description

This PR updates the promo screenshots configuration to use the new backgrounds matching the new brand update (Ntkk0ER4hHt5y9KjEGIiGk-fi-2073_1004)

Testing information

I don't think testing is required here, just code review and check the screenshots below.

Screenshots

(Uses old app screenshots)

---

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr14765-ea08c03
	Version	21.2
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	ea08c03
	App Center Build	WooCommerce - Prototype Builds #12292

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.