Fix ProcessStartInfo tests on CentOS in Debug (#26945)

There is a bug in CentOS7.1 getpwnam_r where it returns the wrong value if you pass in a buffer that is too small to hold the data.  In Debug builds, we are purposefully passing in a buffer that is too small to test the fallback code, which is running into this OS bug.

See https://bugs.centos.org/view.php?id=7324

Fixes #26673

Author: eerhardt

src/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs

@@ -624,13 +624,10 @@ private static (uint userId, uint groupId) GetUserAndGroupIds(ProcessStartInfo s
         private unsafe static (uint? userId, uint? groupId) GetUserAndGroupIds(string userName)
         {
             Interop.Sys.Passwd? passwd;
-#if DEBUG
-            // Use an artificially small buffer in DEBUG to test the fallback path
-            const int BufLen = 2;
-#else
             // First try with a buffer that should suffice for 99% of cases.
+            // Note: on CentOS/RedHat 7.1 systems, getpwnam_r returns 'user not found' if the buffer is too small
+            // see https://bugs.centos.org/view.php?id=7324
             const int BufLen = 1024;
-#endif
             byte* stackBuf = stackalloc byte[BufLen];
             if (TryGetPasswd(userName, stackBuf, BufLen, out passwd))
             {