Plans: Special Offers affect plan layout even when hidden

Quick summary

Context in https://github.com/Automattic/wp-calypso/pull/96631#issuecomment-2518748215

I spotted a visual bug unrelated to this PR ( it's present in production ). For the currency based discount ( MXN, INR, PHP ), there's an excessive amount of space between the plan title and header pricing when switching between 1 year and multi-year term views. This does not happen if the page is initially rendered on a multi-year view.

Steps to reproduce

1. Switch to currency with special offer
2. Navigate to /start/plans?intervalType=yearly
3. Verify that the special offer UI is shown for plans
4. Switch to 2yr or 3yr terms when selecting a different option in the billing term dropdown
5. Verify that the special offer UI still affects layout, even though no special offers are present

What you expected to happen

Special offers shouldn't continue to affect plan layout if no special offers are present

What actually happened

There was excessive whitespace between the plan title and header price

Impact

Some (< 50%)

Available workarounds?

Yes, easy to implement

Start by reproducing the issue at /start/plans?intervalType=yearly with MXN, INR, or PHP, then switch to the 2yr or 3yr billing term. Trace the plan layout and special-offer UI involved in that route. Done means the excessive whitespace no longer appears when the selected term has no special offers, while the offer layout still appears when offers are present.