[scss] SCSS Validator doesn't like brackets

Issue Type: <b>Bug</b> 1. Create an SCSS file 2. Paste this minimal example SCSS into the editor: ``` @mixin change-to-red($ele, $children) { $selector: ''; @each $child in $children { $selector: $selector + $ele + ':nth-child(' + $child + '),'; } #{$selector} { color: red; } } .group { @include change-to-red('p', [1, 2]); } ``` 3. VSC validator will throw several validation errors with: - ] expected [11, 31] - ) expected [11, 35] - at-rule or selector expected [12, 1] VS Code version: Code 1.54.3 (2b9aebd5354a3629c3aba0a5f5df49f43d6689f8, 2021-03-15T10:55:45.459Z) OS version: Windows_NT x64 10.0.19042 <details> <summary>System Info</summary> |Item|Value| |---|---| |CPUs|Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz (16 x 2304)| |GPU Status|2d_canvas: enabled<br>gpu_compositing: enabled<br>multiple_raster_threads: enabled_on<br>oop_rasterization: enabled<br>opengl: enabled_on<br>protected_video_decode: unavailable_off<br>rasterization: enabled<br>skia_renderer: enabled_on<br>video_decode: enabled<br>vulkan: disabled_off<br>webgl: enabled<br>webgl2: enabled| |Load (avg)|undefined| |Memory (System)|31.84GB (17.58GB free)| |Process Argv|--disable-extensions --crash-reporter-id c2837155-db1b-4d81-bfd7-6ed94729a4da| |Screen Reader|no| |VM|0%| </details>Extensions disabled <!-- generated by issue reporter -->