[docs-infra] Missing font in iframe

[oliviertassinari]

Steps to reproduce 🕹

Link to live example:

Steps:

1. Open https://mui.com/material-ui/react-app-bar/#responsive-app-bar-with-drawer

https://github.com/mui/material-ui/blob/20d036754e33ad9f27a45663cedf273884f631c1/docs/data/material/components/app-bar/app-bar.md#L39

Current behavior 😯

See how the font loaded is not Roboto

Expected behavior 🤔

Roboto is used:

Context 🔦

Noticed in https://github.com/mui/material-ui/pull/38684#issuecomment-1699983886

I guess we can fix this in https://github.com/mui/material-ui/blob/20d036754e33ad9f27a45663cedf273884f631c1/docs/src/modules/components/DemoSandbox.js#L19

Your environment 🌎

npx @mui/envinfo

``` Don't forget to mention which browser you used. Output from `npx @mui/envinfo` goes here. ```

[gitstart]

@oliviertassinari we would like to pick this up

[stgeer]

Keen to contribute, and learn! Can you assign this one to me pls?

[danilo-leal]

Pinging you @gitstart as you arrived it first 😬 Feel free to pick this one up!