gh-63016: Skip some mmap tests on FreeBSD

[aisk]

• Issue: "mmap.flush()" is always synchronous, hurting performance #63016

[aisk]

!buildbot freebsd

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @aisk for commit 5151a11 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F143230%2Fmerge

The command will test the builders whose names match following regular expression: freebsd

The builders matched are:

• AMD64 FreeBSD14 PR
• AMD64 FreeBSD PR
• AMD64 FreeBSD Refleaks PR
• AMD64 FreeBSD15 PR

[aisk]

@picnixz Hi, I'm not sure why FreeBSD doesn't support this usage, but I think we can just skip this test as a fix and assume that FreeBSD simply doesn't support m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)?

[picnixz]

I didn't look at the buildbot traceback but if the combination is not supported, I'd prefer checking for an exception being raised.

[aisk]

I have a FreeBSD VM and this is the traceback I got:

$ ./python -m test test_mmap
Using random seed: 1145639683
0:00:00 load avg: 0.85 Run 1 test sequentially in a single process
0:00:00 load avg: 0.85 [1/1] test_mmap
test test_mmap failed -- Traceback (most recent call last):
  File "/usr/home/asaka/cpython/Lib/test/test_mmap.py", line 1176, in test_flush_parameters
    m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 22] Invalid argument

0:00:00 load avg: 0.85 [1/1/1] test_mmap failed (1 error)

== Tests result: FAILURE ==

1 test failed:
    test_mmap

Total duration: 120 ms
Total tests: run=53 skipped=13
Total test files: run=1/1 failed=1
Result: FAILURE

I'm not very familiar with BSD, but I will try to just check the error on FreeBSD. If this is not acceptable, I'll dig into it tomorrow.

[picnixz]

I think catching OSError would be sufficient then. What matters is that we don't crash.