private[this] syntax is deprecated in scala 3.4.x

The generated code will now cause the Scala 3.4.x compiler to emit the warning:

```shell
[warn] 36 | private[this] def argEscape(k: String, v: String): String = Query.apply((k, Some(v))).toString
[warn] | ^
[warn] |Ignoring [this] qualifier.
[warn] |This syntax will be deprecated in the future; it should be dropped.
[warn] |See: https://docs.scala-lang.org/scala3/reference/dropped-features/this-qualifier.html
[warn] |This construct can be rewritten automatically under -rewrite -source 3.4-migration.
```