MWPW-167643: Corrected the number of grid columns for the plans three cards layout

[mirafedas]

Corrected the number of grid columns for the plans variant three cards layout: on the desktop for three cards there should be 3 columns, and for four cards - four columns.

Resolves: MWPW-167643

Test URLs:
Before:

• https://main--cc--adobecom.hlx.page/partnerpromo/square?martech=off
• https://main--milo--adobecom.hlx.page/drafts/mirafedas/three-merch-cards?martech=off
  After:
• https://main--cc--adobecom.hlx.page/partnerpromo/square?martech=off&milolibs=mwpw-167643-three-cards-plans--milo--mirafedas
• https://mwpw-167643-three-cards-plans--milo--mirafedas.hlx.page/drafts/mirafedas/three-merch-cards?martech=off

[aem-code-sync]

	Page	Scores	Audits	Google
📱	/drafts/mirafedas/three-merch-cards?martech=off
🖥️	/drafts/mirafedas/three-merch-cards?martech=off

[github-actions]

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