vfmt: change all '$expr' to '${expr}' (#16428)

vlib/toml/ast/ast.v

@@ -18,8 +18,8 @@ pub mut:
 
 pub fn (r Root) str() string {
 	mut s := typeof(r).name + '{\n'
-	s += '  input:  $r.input\n'
-	s += '  table:  $r.table\n'
+	s += '  input:  ${r.input}\n'
+	s += '  table:  ${r.table}\n'
 	s += '}'
 	return s
 }