Fix intermittent test failures due to SDK issues (#10063)

* Fix intermittent test failures due to SDK issues

* Update dotnet e2e tst

* Revert SDK, ensure build only once

* Remove unused using

Author: jviau

test/WebJobs.Script.Tests.Integration/WebHostEndToEnd/SpecializationE2ETests.cs

@@ -43,9 +43,10 @@ namespace Microsoft.Azure.WebJobs.Script.Tests
 {
     public class SpecializationE2ETests
     {
-        private static SemaphoreSlim _pauseBeforeHostBuild;
-        private static SemaphoreSlim _pauseAfterStandbyHostBuild;
-        private static SemaphoreSlim _buildCount;
+        private static readonly Lazy<int> _buildDotnetIsolated60Path = new(BuildDotnetIsolated60, LazyThreadSafetyMode.ExecutionAndPublication);
+        private static readonly SemaphoreSlim _pauseBeforeHostBuild = new(1, 1);
+        private static readonly SemaphoreSlim _pauseAfterStandbyHostBuild = new(1, 1);
+        private static readonly SemaphoreSlim _buildCount = new(2, 2);
 
         private static readonly string _standbyPath = Path.Combine(Path.GetTempPath(), "functions", "standby", "wwwroot");
         private static readonly string _scriptRootConfigPath = ConfigurationPath.Combine(ConfigurationSectionNames.WebHost, nameof(ScriptApplicationHostOptions.ScriptPath));
@@ -74,10 +75,6 @@ public SpecializationE2ETests(ITestOutputHelper testOutputHelper)
             _environment = new TestEnvironment(settings);
             _loggerProvider = new TestLoggerProvider();
 
-            _pauseBeforeHostBuild = new SemaphoreSlim(1, 1);
-            _pauseAfterStandbyHostBuild = new SemaphoreSlim(1, 1);
-            _buildCount = new SemaphoreSlim(2, 2);
-
             _testOutputHelper = testOutputHelper;
         }
 
@@ -1087,16 +1084,16 @@ private async Task DotNetIsolatedPlaceholderMiss(string scriptRootPath, Action a
             }
         }
 
-        private static void BuildDotnetIsolated60()
+        private static int BuildDotnetIsolated60()
         {
             var p = Process.Start("dotnet", $"build {_dotnetIsolated60Path}/../../..");
             p.WaitForExit();
+            return p.ExitCode;
         }
 
         private IWebHostBuilder InitializeDotNetIsolatedPlaceholderBuilder(string scriptRootPath, params string[] functions)
         {
-            BuildDotnetIsolated60();
-
+            Assert.Equal(0, _buildDotnetIsolated60Path.Value);
             _environment.SetEnvironmentVariable(RpcWorkerConstants.FunctionWorkerRuntimeSettingName, "dotnet-isolated");
             _environment.SetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteUsePlaceholderDotNetIsolated, "1");
             _environment.SetEnvironmentVariable(EnvironmentSettingNames.AzureWebJobsFeatureFlags, ScriptConstants.FeatureFlagEnableWorkerIndexing);