Block Editor Welcome Guide: fix spacing to remove widow

[annezazu]

In reviewing this PR, I noticed that we have widows for each frame of the welcome guide. I don't remember this being the case previously so something must have changed!

Min width of 368px ends up fixing it for the first two (not the library one) but also makes it look a bit too wide:

Rather than making it larger, we could also try shortening each title. The following options appropriately fit into one line:

• Welcome to the block editor > Welcome to the editor
• Make each block your own > Customize each block
• Get to know the block library > Explore all blocks
• Learn how to use the block editor > Learn more

[kristastevens]

Hi @annezazu! Your options are great! They're clear and succinct.