Revive lost synchronized

Author: Duhemm

language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala

@@ -227,7 +227,7 @@ class DottyLanguageServer extends LanguageServer
   override def didChangeWatchedFiles(params: DidChangeWatchedFilesParams): Unit =
     /*thisServer.synchronized*/ {}
 
-  override def didSave(params: DidSaveTextDocumentParams): Unit = {
+  override def didSave(params: DidSaveTextDocumentParams): Unit = thisServer.synchronized {
     val uri = new URI(params.getTextDocument.getUri)
     if (isWorksheet(uri)) {
       if (uri.getScheme == "cancel") {