Wrap use of NSFileProviderManager globalProgress in availability check

This selector was only made available on macOS 11.3
Just to be safe we should check for the availability

Signed-off-by: Claudio Cambra <claudio.cambra@nextcloud.com>

src/gui/macOS/fileproviderdomainsyncstatus_mac.mm

@@ -42,6 +42,7 @@ public:
             return;
         }
 
+        if (@available(macOS 11.3, *)) {
             NSProgress *const downloadProgress = [_manager globalProgressForKind:NSProgressFileOperationKindDownloading];
             NSProgress *const uploadProgress = [_manager globalProgressForKind:NSProgressFileOperationKindUploading];
             _downloadProgressObserver = [[ProgressObserver alloc] initWithProgress:downloadProgress];
@@ -54,6 +55,7 @@ public:
                 updateUpload(progress);
             };
         }
+    }
 
     ~MacImplementation() = default;