Fix LongProcessNamesAreSupported

The process this starts has a long prefix in it's name, eg.
/tmp/#ProcessTests_msso5zem.fzn/123456789012345678901234567890
so match the substring.

Author: gwr

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

@@ -2295,7 +2295,7 @@ public void LongProcessNamesAreSupported()
                 Process[] runningProcesses = Process.GetProcesses();
                 try
                 {
-                    Assert.Contains(runningProcesses, p => p.ProcessName == LongProcessName);
+                    Assert.Contains(runningProcesses, p => p.ProcessName.Contains(LongProcessName));
                 }
                 finally
                 {