test: don't check for code object leaks on 3.13t

Author: nedbat

.github/workflows/python-nightly.yml

@@ -128,4 +128,4 @@ jobs:
 
       - name: "Run tox"
         run: |
-          python -m tox -- -rfsEX
+          python -m tox -v -- -rfsEX

coverage/env.py

@@ -40,6 +40,9 @@
 else:
     PYPYVERSION = (0,)
 
+# Do we have a GIL?
+GIL = getattr(sys, '_is_gil_enabled', lambda: True)()
+
 # Python behavior.
 class PYBEHAVIOR:
     """Flags indicating this Python's behavior."""

tests/test_oddball.py

@@ -210,9 +210,16 @@ def once(x):                                        # line 301
         if fails > 8:
             pytest.fail("RAM grew by %d" % (ram_growth))      # pragma: only failure
 
-    @pytest.mark.skipif(not testenv.C_TRACER, reason="Only the C tracer has refcounting issues")
-    # In fact, sysmon explicitly holds onto all code objects,
-    # so this will definitely fail with sysmon.
+    @pytest.mark.skipif(
+        not testenv.C_TRACER,
+        reason="Only the C tracer has refcounting issues",
+        # In fact, sysmon explicitly holds onto all code objects,
+        # so this will definitely fail with sysmon.
+    )
+    @pytest.mark.skipif(
+        env.PYVERSION[:2] == (3, 13) and not env.GIL,
+        reason = "3.13t never frees code objects: https://github.com/python/cpython/pull/131989",
+    )
     @pytest.mark.parametrize("branch", [False, True])
     def test_eval_codeobject_leak(self, branch: bool) -> None:
         # https://github.com/nedbat/coveragepy/issues/1924