A recent build failed. The original error seemed to be during ci_fetch_deps
where a build message said
```
fatal: reference is not a tree: 346c936e14c6ea3a8d3d65cb1fa46202dc92999d
fatal: Unable to checkout '346c936e14c6ea3a8d3d65cb1fa46202dc92999d' in submodule path 'extmod/ulab'
```
(along with other problems), but this step didn't signal failure to
github actions.
By adding the check= parameter, a failure of the subprocess will cause
a CalledProcessError to be raised, which will make ci_fetch_deps exit with
nonzero status. In turn, this should let Actions understand that something
went wrong with this step, instead of waiting for some subsequent step(s)
to go wrong.
104ac5b965