test: Fix windows_spawn tmp directory cleanup

[xEgoist]

On Windows, a directory that's set as the current working directory is not allowed to be removed. This can cause error on deleteTree if the CWD is set to the handle to be removed and will result in error.FileBusy. However, due to tmp.cleanup() ignoring the errors, the folder removal error will be ignored. (Possibly Related: #15465)

The only test that I found to be violating this is windows_spawn as it sets CWD to the tmp dir then tries to remove it. I added a test to verify this occurrence.

Another option for solving is to always set the CWD to the parent in both cleanup() functions:

zig/lib/std/testing.zig

Lines 520 to 525 in 7285eed

	pub fn cleanup(self: *TmpDir) void {
	self.dir.close();
	self.parent_dir.deleteTree(&self.sub_path) catch {};
	self.parent_dir.close();
	self.* = undefined;
	}

I hate to take another guess, but this * might be * be the last test causing the random CI timeouts on Windows (#14948) as it was also re-enabled on #14647 . However, I believe when #15467 is merged, it could also mitigate these from happening all together.

[squeek502]

This particular case shouldn't have been able to cause the infinite loop in deleteTree (since FileBusy does not trigger a retry), but still good to make sure tmp dirs can be cleaned up.

[xEgoist]

This particular case shouldn't have been able to cause the infinite loop in deleteTree (since FileBusy does not trigger a retry), but still good to make sure tmp dirs can be cleaned up.

Ah, you are right, it shouldn't trigger that, My bad. Thanks for clarifying that.