Can't call load inside of an if statement in Tiltfile

Via k8s slack DM:

Hi, do you know smth about such error during tilt up ?
load statement within a conditional
I have a load inside if condition

I traced it to this issue and resulting commit from Starlark where they recently disallowed loads inside if statements and for statements.

There's at least one Tiltfile out there that depends on this behavior, and probably more. In fact our own Tiltfiles used to depend on this behavior when we had our internal services in microrepos with one Tilt repo to manage them. The Tiltfile would check to see which microrepos are cloned locally, and only if it was present in the expected location on disk would it then load that microrepo's Tiltfile. In fact: we still recommend this setup. We've since moved to a monorepo, but if any customers are using a similar set up their Tiltfiles would now be broken.

Start with how Tiltfile load statements are evaluated, then review the linked Starlark issue and resulting commit. Compare that behavior with the multiple-repository setup described in the issue and determine what compatibility is expected. Done means the documented conditional-load workflow no longer fails during tilt up.