Set COVERAGE_CORE=sysmon

This uses an experimental feature available in Python3.12+. Lets see how
it behaves.

Author: Stormheg

.github/workflows/test.yml

@@ -12,6 +12,7 @@ env:
   TOX_TESTENV_PASSENV: FORCE_COLOR
   PIP_DISABLE_PIP_VERSION_CHECK: "1"
   PIP_NO_PYTHON_VERSION_WARNING: "1"
+  COVERAGE_CORE: sysmon # Only supported on Python 3.12+, ignore on older versions
   PYTHON_LATEST: "3.12"
 
 jobs: