[security] golang.org/x/net/html fix pre-announcement

[Damien Neil]

Hello gophers,

We plan to issue a security fix for the golang.org/x/net/html package in the golang.org/x/net module on Tuesday, August 1.

This will cover CVE-2023-3978.

Following our security policy, this is the pre-announcement for the fix.

- Damien, on behalf of the Go team.