don't import Foundation if FoundationEssentials available

Author: lhoward

Sources/AsyncQueue/CancellableQueue.swift

@@ -20,7 +20,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+import Dispatch
+#else
 import Foundation
+#endif
 
 /// A queue wrapper that enables cancelling all currently executing and pending tasks.
 ///