Git client timeout for checkout operation should be applied to git clean

Similar to JENKINS-29164, except this request is for "git clean" operations.

A Linux build slave with Jenkins workspace on a remote (NFS) file system had frequent build failures due to git client timeout.

We increased the configured git client time limit from 10 to 20, in both "Advanced checkout behaviours" and "Advanced clone behaviors".

The git client timeout error occured less often, but it still happens occasionally in "git clean" (we use the "Clean After Checkout" Git behaviour). The console log shows that git clean gets a timeout value of 10 (the default), not 20 (our configured value).

If the user-specified git client timeout value is applied to git checkout, then it should also be applied to git clean. Both git operations are vulnerable to file system slowdowns.

Thanks!