Fix CWD race: add [Collection] to serialize CWD-mutating tests

Parity tests that call Directory.SetCurrentDirectory() race with each
other when xUnit runs test classes in parallel. Adding
[Collection("CWD-Dependent")] serializes these 4 test classes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SimaTian

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAProcessFrameworkReferencesMultiThreading.cs

@@ -10,6 +10,8 @@
 
 namespace Microsoft.NET.Build.Tasks.UnitTests
 {
+    [Collection("CWD-Dependent")]
+
     public class GivenAProcessFrameworkReferencesMultiThreading
     {
         [Fact]

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAResolveRuntimePackAssetsMultiThreading.cs

@@ -10,6 +10,8 @@
 
 namespace Microsoft.NET.Build.Tasks.UnitTests
 {
+    [Collection("CWD-Dependent")]
+
     public class GivenAResolveRuntimePackAssetsMultiThreading
     {
         [Fact]

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAResolveTargetingPackAssetsMultiThreading.cs

@@ -10,6 +10,8 @@
 
 namespace Microsoft.NET.Build.Tasks.UnitTests
 {
+    [Collection("CWD-Dependent")]
+
     public class GivenAResolveTargetingPackAssetsMultiThreading
     {
         [Fact]

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAShowMissingWorkloadsMultiThreading.cs

@@ -10,6 +10,8 @@
 
 namespace Microsoft.NET.Build.Tasks.UnitTests
 {
+    [Collection("CWD-Dependent")]
+
     public class GivenAShowMissingWorkloadsMultiThreading
     {
         [Fact]