`"#$-1"` interpreted as shorthand global interpolation, is just a string literal

```rb
puts "#$-1" => # "\#$-1"
```

```rb
# Current:
s(:dstr,
  s(:gvar, :$-1))
# I would expect:
s(:str, "\#$-1")
```

Uncertain of the rules, it seems to be a valid global variable name :shrug: 