github_packages: update mediaType.
github_packages: update mediaType.

This custom type will allow better display in GitHub Packages.

EricFromCanada/brew,MikeMcQuaid/brew,sjackman/homebrew,vitorgalvao/brew,claui/brew,JCount/brew,sjackman/homebrew,sjackman/homebrew,JCount/brew,claui/brew,EricFromCanada/brew,Homebrew/brew,MikeMcQuaid/brew,EricFromCanada/brew,claui/brew,claui/brew,MikeMcQuaid/brew,EricFromCanada/brew,nandub/brew,Homebrew/brew,vitorgalvao/brew,nandub/brew,nandub/brew,vitorgalvao/brew,Homebrew/brew,vitorgalvao/brew,JCount/brew,Homebrew/brew,JCount/brew,sjackman/homebrew,nandub/brew,MikeMcQuaid/brew