Update Discord logo (#29285)

Fixes #27057 by changing the discord .svg file and running `make svg`.

Before:

<img width="637"
src="https://private-user-images.githubusercontent.com/85847352/267667100-1eaf5d20-b4e9-4736-bb55-7f1da04bbde7.png?jwt=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.C6jVQLFPfq4fhGV8wiY9D-P21PUNTDMkX2d2-kU17Ug">

After:

<img width="637"
src="https://github.com/go-gitea/gitea/assets/106393991/45b197ae-e422-42f4-999e-25dc8f6b7a92">