Ensure no InvalidCastException is happening in enumeration

Author: AlexanderSher

src/LanguageServer/Impl/Implementation/Server.cs

@@ -649,7 +649,7 @@ private async Task OnDocumentChangeProcessingCompleteAsync(IDocument doc, Versio
 
                 if (doc is ProjectEntry entry) {
                     var reanalyzeEntries = Analyzer.GetEntriesThatImportModule(entry.ModuleName, false);
-                    foreach (IDocument d in reanalyzeEntries) {
+                    foreach (var d in reanalyzeEntries.OfType<IDocument>()) {
                         await EnqueueItemAsync(d, parse: false);
                     }
                 }