bpo-35967: Skip test with `uname -p` on Android (GH-19577)

The uname binary on Android does not support -p [1]. Here is a sample
log:
```
0:06:03 load avg: 0.56 [254/421/8] test_platform failed -- running: test_asyncio (5 min 53 sec)
uname: Unknown option p (see "uname --help")
test test_platform failed -- Traceback (most recent call last):
  File "/data/local/tmp/lib/python3.9/test/test_platform.py", line 170, in test_uname_processor
    proc_res = subprocess.check_output(['uname', '-p'], text=True).strip()
  File "/data/local/tmp/lib/python3.9/subprocess.py", line 420, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/data/local/tmp/lib/python3.9/subprocess.py", line 524, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['uname', '-p']' returned non-zero exit status 1.
```
[1] https://android.googlesource.com/platform/external/toybox/+/refs/heads/master/toys/posix/uname.c

Automerge-Triggered-By: @jaraco