Make "VS 17.6" darc channel promotionable

[missymessa]

• This issue is blocking
• This issue is causing unreasonable pain

Same thing as ce6d3d3

Release Note Category

• Feature changes/additions
• Bug fixes
• Internal Infrastructure Improvements

Release Note Description

Newly created "VS 17.6" darc channel can be used for promotions.

[missymessa]

PR: #12151