[go] Use lighter branding logo

[rcalixte]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created either the topic I am modifying/adding or the collection entry I am modifying/adding.

Which change are you proposing?

• Suggesting edits to an existing topic or collection

---

Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)

The black version of the logo has difficulties being seen on dark backgrounds. The "Gopher Blue" version of the logo from the official branding has better visibility on either dark or light backgrounds.

---

Please note: we will close your PR without comment if you do not check the boxes above and provide ALL requested information.

[ahpook]

Cool, thanks for the update.