skip projects that don't support workloads during workload restore

Author: baronfel

src/Cli/dotnet/commands/dotnet-workload/restore/WorkloadRestoreCommand.cs

@@ -44,23 +44,29 @@ public override int Execute()
             return 0;
         }
 
+        private static string GetRequiredWorkloadsTargetName = "_GetRequiredWorkloads";
+
         private List<WorkloadId> RunTargetToGetWorkloadIds(IEnumerable<string> allProjects)
         {
             var globalProperties = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
             {
                 {"SkipResolvePackageAssets", "true"}
             };
 
+
             var allWorkloadId = new List<WorkloadId>();
             foreach (string projectFile in allProjects)
             {
                 var project = new ProjectInstance(projectFile, globalProperties, null);
+                if (!project.Targets.ContainsKey(GetRequiredWorkloadsTargetName))
+                {
+                    continue;
+                }
 
-                bool buildResult = project.Build(new[] { "_GetRequiredWorkloads" },
-                    loggers: new ILogger[]
-                    {
+                bool buildResult = project.Build([GetRequiredWorkloadsTargetName],
+                    loggers: [
                         new ConsoleLogger(Verbosity.ToLoggerVerbosity())
-                    },
+                    ],
                     remoteLoggers: Enumerable.Empty<ForwardingLoggerRecord>(),
                     targetOutputs: out var targetOutputs);
 
@@ -73,7 +79,7 @@ private List<WorkloadId> RunTargetToGetWorkloadIds(IEnumerable<string> allProjec
                         isUserError: false);
                 }
 
-                var targetResult = targetOutputs["_GetRequiredWorkloads"];
+                var targetResult = targetOutputs[GetRequiredWorkloadsTargetName];
                 allWorkloadId.AddRange(targetResult.Items.Select(item => new WorkloadId(item.ItemSpec)));
             }