Auto merge of #10724 - ehuss:ci-disk-space, r=Eh2406

Auto merge of #10724 - ehuss:ci-disk-space, r=Eh2406

Clear disk space on CI.

Cargo's testsuite uses a considerable amount of disk space. On windows-gnu, the target directory can get over 12GB, and there is only 13GB free.  We're starting to run out of disk space, so this is a stop-gap that clears out the test data before running the smoke test which uses a fair bit of space itself.

We will probably need to think about addressing #9701 somehow, otherwise we will start running out of space as we add more tests. See the linked issues in https://github.com/rust-lang/cargo/pull/9701#issuecomment-881765517 for additional context.