Increase external data timeout

[thomashampson]

Description of work

Increase external data download timeout from 600 o 1200 seconds. It timed out on a ~250 mb file, so I double it to give it a chance to download a ~500 mb file.

There is no associated issue.

To test:

External data should download in the linux PR check.

This does not require release notes because it's a change to cmake config

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[sf1919]

I'm a bit confused by this as I thought the failure in the docs had been resolved in #37908

[jhaigh0]

Linux PR job passed. The doctest failure is clearly unrelated. This PR is needed to fix at leat one other.