fmt: don't break indexing in string interpolation. (#10195)

vlib/v/ast/str.v

@@ -180,7 +180,7 @@ pub fn (lit &StringInterLiteral) get_fspec_braces(i int) (string, bool) {
 					} else if sub_expr.left is CallExpr {
 						sub_expr = sub_expr.left
 						continue
-					} else if sub_expr.left is CastExpr {
+					} else if sub_expr.left is CastExpr || sub_expr.left is IndexExpr {
 						needs_braces = true
 					}
 					break

vlib/v/fmt/tests/string_interpolation_keep.vv

@@ -7,9 +7,11 @@ fn main() {
 	b := 'xyz'
 	e := 'a: $a b: $b i: $i'
 	d := 'a: ${a:5s} b: ${b:-5s} i: ${i:20d}'
+	f := 'a byte string'.bytes()
 	println('a: $a $b xxx')
 	eprintln('e: $e')
 	_ = ' ${foo.method(bar).str()} '
 	println('(${some_struct.@type}, $some_struct.y)')
 	_ := 'CastExpr ${int(d.e).str()}'
+	println('${f[0..4].bytestr()}')
 }