test: an obscure test is more unpredictable: skip it

tests/test_arcs.py

@@ -1851,7 +1851,11 @@ def test_lambda_in_dict(self) -> None:
         )
 
 
-xfail_eventlet_670 = pytest.mark.xfail(
+# This had been a failure on Mac 3.9, but it started passing on GitHub
+# actions (running macOS 12) but still failed on my laptop (macOS 14).
+# I don't understand why it failed, I don't understand why it passed,
+# so just skip the whole thing.
+skip_eventlet_670 = pytest.mark.skipif(
     env.PYVERSION[:2] == (3, 9) and env.CPYTHON and env.OSX,
     reason="Avoid an eventlet bug on Mac 3.9: eventlet#670",
     # https://github.com/eventlet/eventlet/issues/670
@@ -1861,7 +1865,7 @@ def test_lambda_in_dict(self) -> None:
 class AsyncTest(CoverageTest):
     """Tests of the new async and await keywords in Python 3.5"""
 
-    @xfail_eventlet_670
+    @skip_eventlet_670
     def test_async(self) -> None:
         self.check_coverage("""\
             import asyncio
@@ -1888,7 +1892,7 @@ async def print_sum(x, y):                      # 8
         )
         assert self.stdout() == "Compute 1 + 2 ...\n1 + 2 = 3\n"
 
-    @xfail_eventlet_670
+    @skip_eventlet_670
     def test_async_for(self) -> None:
         self.check_coverage("""\
             import asyncio
@@ -1985,7 +1989,7 @@ async def async_test():
 
     # https://github.com/nedbat/coveragepy/issues/1176
     # https://bugs.python.org/issue44622
-    @xfail_eventlet_670
+    @skip_eventlet_670
     def test_bug_1176(self) -> None:
         self.check_coverage("""\
             import asyncio