Blocks: update CLI to only input strings in descriptions

[jeherve]

See #26792

Proposed changes:

Let's not encourage the use of non-strings in block descriptions; only strings should be used from now on.

Other information:

• Have you written new tests for your changes, if applicable?
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Jetpack product discussion

• N/A

Does this pull request change what data or activity we track or use?

• No

Testing instructions:

• Not much to test here, but you could try to run jetpack docker wp jetpack scaffold block something and check the files being created.

[github-actions]

Are you an Automattician? You can now test your Pull Request on WordPress.com. On your sandbox, run

bin/jetpack-downloader test jetpack update/block-skeleton

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[github-actions]

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[bindlegirl]

@jeherve I see #29757 is blocked. Should this PR wait for a decision on the first one?

[jeherve]

Should this PR wait for a decision on the first one?

I think we could proceed with this, it will ensure that at least, we will not have more blocks added in the next few weeks / months that we'll need to modify.

[bindlegirl]

Thanks for clarifying. LGTM