Workaround flaky ProcessName behavior during process startup

Reenable long Process.Name test on OSX

Fixes dotnet#111460
Fixes dotnet#29330

src/libraries/System.Diagnostics.Process/tests/ProcessTests.cs

@@ -2264,7 +2264,6 @@ public void TestLongProcessIsWorking()
         }
 
         [PlatformSpecific(TestPlatforms.AnyUnix)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/29330", TestPlatforms.OSX)]
         [Fact]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/52852", TestPlatforms.MacCatalyst)]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/53095", TestPlatforms.Android)]
@@ -2294,6 +2293,10 @@ public void LongProcessNamesAreSupported()
 
             using (Process px = Process.Start(sleepCommandPathFileName, "600"))
             {
+                // Reading of long process names is flaky during process startup and shutdown.
+                // Wait a bit to skip over the period where the ProcessName is not reliable.
+                Thread.Sleep(100);
+
                 Process[] runningProcesses = Process.GetProcesses();
                 try
                 {