Unquote variable false negative in brace expansion in array

[A4-Tacks]

For bugs with existing features

• Rule Id: SC2206
• My shellcheck version: 0.10.0
• [x] The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC2086)
• [ ] I tried on https://www.shellcheck.net/ and verified that this is still a problem on the latest commit

Here's a snippet or screenshot that shows the problem:

#!/bin/bash
_x=({$VAR,$VAR})

Here's what shellcheck currently says:

No says

Here's what I wanted or expected to see:

_x=({$VAR,$VAR})
     ^--^ SC2206 (warning): Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.
          ^--^ SC2206 (warning): Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.