[tests] ValidateApplicationSamples: use a temporary path for generating the manifest

Other tests also generate and use `postgres.module.bicep` in the tests'
bindir, and these can run in parallel causing them to interfere with
each other.

Issue: #5174

Author: radical

tests/Aspire.Hosting.Tests/Schema/SchemaTests.cs

@@ -195,7 +195,8 @@ public void ValidateApplicationSamples(string testCaseName, Action<IDistributedA
     {
         _ = testCaseName;
 
-        var builder = TestDistributedApplicationBuilder.Create(["--publisher", "manifest", "--output-path", "not-used.json"]);
+        string manifestDir = Directory.CreateTempSubdirectory(testCaseName).FullName;
+        var builder = TestDistributedApplicationBuilder.Create(["--publisher", "manifest", "--output-path", Path.Combine(manifestDir, "not-used.json")]);
         builder.Services.AddKeyedSingleton<IDistributedApplicationPublisher, JsonDocumentManifestPublisher>("manifest");
         configurator(builder);