Handle details of any type in core.PlatformUpgrade() status

The status details of the function are used to identify the specific cause of a non-nil status. This is done via a type
assertion. Previously, this type assertion was configured such that a details of any type other than the expected would
result in a panic. At the moment, that will not occur because we only add details of one type. However, the whole point
of the type assertion is to support details of multiple types, and if other types are added a panic will not be the
appropriate behavior.

A better approach is to check the result of the type assertion, handling the non-nil status as a generic error if its
details are of a different type.

cli/core/upgrade.go

@@ -94,9 +94,14 @@ func runUpgradeCommand(cmd *cobra.Command, args []string) {
 		}
 
 		_, err := core.PlatformUpgrade(context.Background(), r, output.ProgressBar(), output.TaskProgress())
-		if d := err.Details(); len(d) > 0 && d[0].(*rpc.AlreadyAtLatestVersionError) != nil {
-			feedback.Printf("Platform %s is already at the latest version", platformRef)
-		} else if err != nil {
+		if err != nil {
+			if d := err.Details(); len(d) > 0 {
+				if _, ok := d[0].(*rpc.AlreadyAtLatestVersionError); ok {
+					feedback.Printf("Platform %s is already at the latest version", platformRef)
+					continue
+				}
+			}
+
 			feedback.Errorf("Error during upgrade: %v", err)
 			os.Exit(errorcodes.ErrGeneric)
 		}