For some reason, gvim is adding one extra pixel of spacing after each character. It almost seems similar to this question, but in my case gvim does use the correct font.
I compared the same font in my terminal and gvim (see below, top = terminal, bottom = gvim, just for testing with an empty
.vimrc file), the individual characters are identical (same font/width/height/..), but after each character there is an additional pixel of spacing. Any idea why this is happening and how I can fix this?