fix: only use "sysmon" core when available (Python 3.12+) (#1747)

* Only use sysmon core when available (Python 3.12+)

* Update test case for both with and without SysMonitor

coverage/collector.py

@@ -150,6 +150,10 @@ def __init__(
             core = "pytrace"
         else:
             core = os.getenv("COVERAGE_CORE")
+
+            if core == "sysmon" and not env.PYBEHAVIOR.pep669:
+                core = None
+
             if not core:
                 # Once we're comfortable with sysmon as a default:
                 # if env.PYBEHAVIOR.pep669 and self.should_start_context is None:

tests/test_process.py

@@ -1122,15 +1122,17 @@ def test_core_request_pytrace(self) -> None:
         core = re_line(r" core:", out).strip()
         assert core == "core: PyTracer"
 
-    @pytest.mark.skipif(not env.PYBEHAVIOR.pep669, reason="No sys.monitoring to request")
     def test_core_request_sysmon(self) -> None:
         self.del_environ("COVERAGE_TEST_CORES")
         self.set_environ("COVERAGE_CORE", "sysmon")
         self.make_file("numbers.py", "print(123, 456)")
         out = self.run_command("coverage run --debug=sys numbers.py")
         assert out.endswith("123 456\n")
         core = re_line(r" core:", out).strip()
-        assert core == "core: SysMonitor"
+        if env.PYBEHAVIOR.pep669:
+            assert core == "core: SysMonitor"
+        else:
+            assert core in ("core: CTracer", "core: PyTracer")
 
 
 class FailUnderNoFilesTest(CoverageTest):