fix CHANGELOG.md for 0.23.0

[eyusufatik]

The mentioned commit in the changelog is this: c1bb316

Change looks unnecessary, however, I had a minor heart-attack once I saw the changelog because we've been using the global-context feature for some time.

[apoelstra]

Yep, good catch!

And for what it's worth, I hate this name global-context-less-secure. The "less secure" global context is only "less secure" assuming a cascade of other failures which we have no evidence have ever happened, and assuming a physical attacker who can produce hundreds or thousands of signatures. So I apologize for your moment of panic.

[apoelstra]

ACK 4b00c71; successfully ran local tests