fix: generate FALSE instead of expr in () conditions

[Globidev]

This is an attempt at fixing #4595

Disclaimer: Pretty fluent in Rust but I just discovered the codebase, so I probably missed a bunch of things.
I guess we'll want to add tests, and I'll likely need some directions as to where exactly to put them :)

[max-sixty]

Awesome @Globidev ! Nice work.

We can add a test next to

prql/prqlc/prqlc/tests/integration/sql.rs

Lines 1213 to 1226 in 6b4c438

	#[test]
	fn test_not_in_values() {
	assert_snapshot!((compile(r#"
	from employees
	filter !(title | in ["Sales Manager", "Sales Support Agent"])
	"#).unwrap()), @r#"
	SELECT
	*
	FROM
	employees
	WHERE
	NOT title IN ('Sales Manager', 'Sales Support Agent')
	"#);
	}

Then running cargo insta test --accept (or task test-rust) will fill in the generated SQL.

[max-sixty]

A changelog entry would be nice but not strictly required

[Globidev]

Thanks a bunch for the pointers!

Feel free to point out anything that would be missing or need tweaking

[max-sixty]

Super, thanks @Globidev !