Cannot set --affinity option for 32+ CPUs

I am trying to use `--affinity` parameter to run System.Net.Security microbenchmarks. It works fine for <32 CPUs but when I try
`--platform x64 --affinity 4294967295` (0xFFFFFFFF) to set the affinity to 32 CPUs I get this error:

```
MicroBenchmarks 1.0.0-dev
© Microsoft Corporation. All rights reserved.

ERROR(S):
Option 'affinity' is defined with a bad format.
USAGE:
...
```
I am assuming even I am setting `--platform x64`, the MicroBenchmarks app is running as AnyCPU or x86 platform, and that is why I am getting the error.

Any ideas on how to fix this?

Additional info:
```
$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 52 bits physical, 57 bits virtual
CPU(s): 56
On-line CPU(s) list: 0-55
Thread(s) per core: 1
Core(s) per socket: 56
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 143
Model name: Intel(R) Xeon(R) Platinum 8480+
...

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.6 LTS
Release: 20.04
Codename: focal
```