loading/syntax-versioning: Lookup syntax version in latest world (#60691)
Syntax versioning (intentionally) uses a binding partitioned constant to
set the syntax version. This gives well defined meaning to changing the
parser of the course of a module's lifetime, but open's up the question
which world age `include` uses to determine the syntax version. I think
the correct answer is that `include` should look at the latest world
age, since it also implicitly raises the world age for the statements it
executes, so it would be somewhat inconsistent for the parse to happen
in the caller's world age. Fixes #60624. Also addresses a somewhat
hilarious interaction with backdating where the syntax version depended
on the value of `--depwarn` (causing test failures in #60481).
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Co-authored-by: Keno Fischer <Keno@users.noreply.github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>