[BUG] giscus theme is different from FixIt theme when initialize

[Bendancom]

在 giscus 初始化时因未修改其中 <script> 元素中的 data-theme 属性，导致其仍为默认的 preferred_color_scheme，会被自动推导至 dark 主题。 the attribute:data-theme in the <script> element isn't modified when the giscus initialize,which leads to the content of data-theme is also in default which is preferred_color_scheme and it automatically infer to dark theme.

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[Lruihao]

暂时无法复现，网络不太好的时候是无法切换的。