Bad error message for ? : and tuple

```julia
julia> true ? 1, 2 : 3
ERROR: ParseError:
# Error @ REPL[1]:1:9
true ? 1, 2 : 3
# └ ── space required before `:` in `?` expression
Stacktrace:
[1] top-level scope
@ REPL:1
```

Reproduce the Julia REPL input `true ? 1, 2 : 3` and inspect the resulting ParseError and its highlighted location. Determine what wording would accurately explain this tuple-and-ternary syntax case; done means the diagnostic is corrected and the same input is covered by an appropriate parser test.

Written by the indexing model from the issue text.