docs: update reference documentation to reflect type definition correctly

[abiriadev]

Hi Vitepress team. Thank you for this wonderful project!

I found some differences between Site Config reference documentation and its actual type definition while reading the document, so I made changes to reflect the differences.

For example:

Document:

vitepress/docs/reference/site-config.md

Line 483 in 7dbeac6

languages?: Shiki.ILanguageRegistration

Actual type:

vitepress/src/node/markdown/markdown.ts

Line 54 in 7dbeac6

languages?: ILanguageRegistration[]

Document:

vitepress/docs/reference/site-config.md

Line 494 in 7dbeac6

allowedAttributes?: string[]

Actual type:

vitepress/src/node/markdown/markdown.ts

Line 46 in 7dbeac6

allowedAttributes?: Array<string | RegExp>

Document:

vitepress/docs/reference/site-config.md

Line 507 in 7dbeac6

headers?: HeadersPluginOptions

Actual type:

vitepress/src/node/markdown/markdown.ts

Line 51 in 7dbeac6

headers?: HeadersPluginOptions | boolean

Document:

vitepress/docs/reference/site-config.md

Line 534 in 7dbeac6

math?: any

Actual type:

vitepress/src/node/markdown/markdown.ts

Line 59 in 7dbeac6

math?: boolean | any

Regards.