Fix: Multiple block warning min height.

[jorgefilipecosta]

Description

The min-height style, for multiple block warnings, was not correct and the design was not right.

How has this been tested?

I pasted the following string in the code editor:

<!-- wp:subhead -->
<p class="wp-block-subhead">Subhead 1</p>
<!-- /wp:subhead -->

<!-- wp:subhead -->
<p class="wp-block-subhead">Subhead 2</p>
<!-- /wp:subhead -->

I checked the design of the multiple block warning looks good.

Screenshots

Before:

After:

[jasmussen]

Interesting, I'm not seeing your "after" image when I try this branch. I'm seeing this:

Which looks good to me, by the way, but wanted to note.

Also, I'm seeing a JS error when trying to save after the fact. Am I doing something wrong?

nonce.js:18 Uncaught (in promise) TypeError: Cannot read property 'addAction' of undefined
    at nonce.js:18
    at next (index.js:93)
    at root-url.js:33
    at namespaceAndEndpointMiddleware (namespace-endpoint.js:21)
    at root-url.js:11
    at next (index.js:93)
    at preloading.js:43
    at next (index.js:93)
    at apiFetch (index.js:96)
    at _callee$ (posts.js:130)

See also #7741

[jorgefilipecosta]

Sorry, @jasmussen this PR was old and things change very fast. This PR was rebased with auto merge so I did not retest everything wrongly assuming it was still valid.
I think the new design can still benefit from an update to the min-height, so I updated this PR and the before and after images.
Regarding the error, I'm not being able to reproduce it this was rebased again before my tests could you please check if the error is still happening?
Thank you a lot for the review!

[jasmussen]

Now seeing this:

This looks good, nice work! Also, the JS errors appear to be related to my dev env. Probably cache or something. Nice work!