ensure that the italic font has the same weight as the normal font

The specified font[] pattern need not have a medium weight. It could be
specified as a number too or have a different weight other than medium.

Signed-off-by: Christoph Lohmann <20h@r-36.net>
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Internal Server Error - Gitea: Git with a cup of tea and freedom
500 Internal Server Error

Gitea Version: 1.28.0+dev-505-g31b4d79a84