chore: add markdown plugin back · sanity-io/sanity@831fff1

ubuntu-latest pipelines will use ubuntu-24.04 soon. For more details, see https://github.com/actions/runner-images/issues/10636

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)

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