Improve FormatExprCall dummy (#5290)

This solves an instability when formatting cpython. It also introduces
another one, but i think it's still a worthwhile change for now.

There's no proper testing since this is just a dummy.

crates/ruff_python_formatter/src/lib.rs

@@ -247,12 +247,12 @@ mod tests {
         let input = r#"
 # preceding
 if    True:
-    print( "hi" )
+    pass
 # trailing
 "#;
         let expected = r#"# preceding
 if True:
-    NOT_IMPLEMENTED_call()
+    pass
 # trailing
 "#;
         let actual = format_module(input)?.as_code().to_string();