Skip unpacking unsupported platforms (#127)

This is a more appropriate fix for
https://github.com/apple/container/issues/61 - which was closed by use
of a workaround.
There is no need to unpack image variants that we dont support.

Signed-off-by: Aditya Ramani <a_ramani@apple.com>

Sources/Services/ContainerImagesService/Server/SnapshotStore.swift

@@ -62,6 +62,9 @@ public actor SnapshotStore {
             guard let platform = desc.platform else {
                 throw ContainerizationError(.internalError, message: "Missing platform for descriptor \(desc.digest)")
             }
+            guard Self.shouldUnpackPlatform(platform) else {
+                continue
+            }
             let currentSubTask = await taskManager.startTask()
             if let progressUpdate {
                 let _taskUpdateProgress = ProgressTaskCoordinator.handler(for: currentSubTask, from: progressUpdate)
@@ -183,6 +186,13 @@ public actor SnapshotStore {
         try self.fm.createDirectory(at: uniqueDirectoryURL, withIntermediateDirectories: true, attributes: nil)
         return uniqueDirectoryURL
     }
+
+    private static func shouldUnpackPlatform(_ platform: Platform) -> Bool {
+        guard platform.os == "linux" else {
+            return false
+        }
+        return true
+    }
 }
 
 extension FileManager {