python3Packages.uvloop: disable problematic test on aarch64

[mweinelt]

Motivation for this change

This test case gets stuck on our aarch64 builder since the 0.15.0
upgrade, and so the package has not been in the cache for aarch64,
since the job reliably timed out.

The issue didn't get noticed earlier because the package does in fact
build on some aarch64 machines, like my raspberry pi 4.

Reported upstream at MagicStack/uvloop#412.

ZHF #122042

cc #118770

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS (literally tested on the hydra builder that reproducibly got stuck on this test)
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

============================= test session starts ==============================
platform linux -- Python 3.8.9, pytest-6.2.3, py-1.10.0, pluggy-0.13.1
rootdir: /build/tmp.Tl3h685wCE
collected 489 items / 1 deselected / 488 selected                              

tests/test_aiohttp.py ....
tests/test_base.py ...............................................................................s...
tests/test_context.py ..................s....s......
tests/test_cython.py .
tests/test_dealloc.py .
tests/test_dns.py ....................s..............................
tests/test_executors.py ....
tests/test_pipes.py ............
tests/test_process.py ...............................................................................
tests/test_process_spawning.py .
tests/test_regr1.py .
tests/test_signals.py s...................
tests/test_sockets.py ...............s.........ss..s.....
tests/test_tcp.py ..............................s.................................................s.s.ss.ssssss..s..ssssssss
tests/test_testbase.py ...
tests/test_udp.py .......................
tests/test_unix.py ..................................

=============================== warnings summary ===============================
../../nix/store/z5jg2q4h3smqfbxddsnxg25h89g6088p-python3.8-pytest-6.2.3/lib/python3.8/site-packages/_pytest/config/__init__.py:1183
  /nix/store/z5jg2q4h3smqfbxddsnxg25h89g6088p-python3.8-pytest-6.2.3/lib/python3.8/site-packages/_pytest/config/__init__.py:1183: PytestDeprecationWarning: The --strict option is deprecated, use --strict-markers instead.
    self.issue_config_time_warning(

-- Docs: https://docs.pytest.org/en/stable/warnings.html
===== 459 passed, 29 skipped, 1 deselected, 1 warning in 118.16s (0:01:58) =====
/build/uvloop-0.15.2
Finished executing pytestCheckPhase
pytestcachePhase
/nix/store/mpcpl3ml06x0p3ac76f74yl32xwp0kmj-python3.8-uvloop-0.15.2

[mweinelt]

Using --deselect, since there are two test with the same name.