another vfmt2 fix

vlib/v/fmt/tests/string_interpolation_literal_keep.vv

@@ -5,9 +5,9 @@ fn main() {
 	i := 123
 	a := 'abc'
 	b := 'xyz'
-	c := 'a: $a b: $b i: $i'
+	e := 'a: $a b: $b i: $i'
 	d := 'a: ${a:5s} b: ${b:-5s} i: ${i:20d}'
 	println('a: $a $b xxx')
-	eprintln('c: $c .')
+	eprintln('e: $e')
 	println(d)
 }