Update F# language color according to the language icon

[64J0]

Description

The F# icon color is mostly blue (https://en.wikipedia.org/wiki/F_Sharp_(programming_language)):

But the language color on GitHub is pink/purple:

I'm sending this PR to better align the icon color with the GitHub language color.

Checklist:

• I am changing the color associated with a language
  • I have obtained agreement from the wider language community on this color change.
    • URL to public discussion: About changing F# language color on GitHub to be more aligned to the language icon dotnet/fsharp#16563
    • Optional: URL to official branding guidelines for the language: https://en.wikipedia.org/wiki/F_Sharp_(programming_language)

[lildude]

Cross-referencing the discussion at #6701 (comment)