Update SSO template headline

[nadonomy]

Apologies I missed submitting this while reviewing in GitHub (PEBKAC):

https://github.com/matrix-org/synapse/pull/12210/files/be023cad8c82149a60d30c09c9897392876f036d#diff-6360959f39ea2113790941f7332d3511bf4a9667659e7710c8e60a253b227563

The h1/headline in the SSO template should be 'Choose your account name' not 'Choose your user name'.

[callahad]

This is a fixup / refinement to #12210 in addressing #12205.

Let's get it into the 1.55 final, so we don't have to tweak that copy twice in subsequent releases.

[babolivier]

Ah, sorry. That was deliberate because an "account name" doesn't mean anything to me as a user (but "user name" does). But fair enough if that doesn't make sense.

[nadonomy]

@babolivier For ref we're navigating Apple's review process and so are trying to be exact in the nomenclature in the copy.

It's my bad for failing to submit the PR comment feedback, and failing to keep an eye on follow up. But, any time we're working on Sign In With Apple I think we'd benefit from in depth discussion/agreement any time we're straying from the issue requirements.

In this case, we're betting on the specific combination of 'account name' as meaningful jargon, and 'This is required...' in micro copy to make it explicit the data is required and not optional.

Hopefully this gets us through!

[DMRobertson]

#12260 was committed to the release branch, then manually merged into develop in 0a59f97.

[babolivier]

But, any time we're working on Sign In With Apple I think we'd benefit from in depth discussion/agreement any time we're straying from #12205.

Agreed, and I thought you had validated this straying from it initially, but my bad for not pointing it out specifically when I asked you for review - sorry about that!