encoding/json: adjust comment about encoding \b and \f

The encoding for the control characters \b and \f was
changed in http://go.dev/cl/521675. This CL adjusts the
corresponding comment about encoding bytes < 0x20.

Change-Id: I83b7311e4fa0731f6601ca64a66042425b4cecac
Reviewed-on: https://go-review.googlesource.com/c/go/+/523435
Reviewed-by: Ian Lance Taylor <[email protected]>
Run-TryBot: Joseph Tsai <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Joseph Tsai <[email protected]>

Author: hoeppi-google

src/encoding/json/encode.go

@@ -980,7 +980,7 @@ func appendString[Bytes []byte | string](dst []byte, src Bytes, escapeHTML bool)
 			case '\t':
 				dst = append(dst, '\\', 't')
 			default:
-				// This encodes bytes < 0x20 except for \t, \n and \r.
+				// This encodes bytes < 0x20 except for \b, \f, \n, \r and \t.
 				// If escapeHTML is set, it also escapes <, >, and &
 				// because they can lead to security holes when
 				// user-controlled strings are rendered into JSON