Add more resolutions to gitg.ico to fix blurry shortcuts in High DPI

In High DPI monitors the icon is blurred due to a single 32x32 size being inside the .ico file. This adds more resolutions to the file as recommended by https://learn.microsoft.com/en-us/windows/apps/design/style/iconography/app-icon-construction using this SVG as source https://gitlab.gnome.org/GNOME/gitg/raw/master/data/icons/org.gnome.gitg.svg

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