gitea-plugin: fix test

The test seems to be broken for a while[1]. The cause for this is that in gitea 1.14 the create-user command got renamed to user create.

[1] https://hydra.nixos.org/build/151092299

Created by  Maximilian Bosch  on August 28, 2021
25T4FPHIKRJUPFBIPZJPE2CMVYFPNOP6ZJEPTMDEL6C5S6JGH7YAC
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