Disable timestamp fetching during build

[Firgrep]

We're getting a bunch of warnings that Nextra is unable to get the timestamp during CI build, however, we'd like to turn these off entirely since all files are being modified during the pipeline.

There is something about disabling it for the page here but will it still attempt to fetch the timestamp during build?

https://nextra.site/docs/docs-theme/built-ins/layout#last-updated-date

Cheers