ci(tests): suppress CPython 3.12 interned-unicode leak (PyUnicode_New) in sanitizer runs

Under ASan/LSan with Python 3.12 on Ubuntu 22.04/24.04, the cleanup tests
report direct leaks rooted in CPython’s unicode interning path (frames via
PyUnicode_New) during module import in our embedded init.

This is a known CPython issue (python/cpython#113190). Interned-unicode
cleanup was re-enabled in 3.13 (python/cpython#113601) but not backported
to 3.12. To keep CI signal meaningful while we still test against 3.12,
enable a narrow LSan suppression for PyUnicode_New only, and only on 3.12.

Notes:
- detect_leaks=1 remains enabled; the suppression is limited to PyUnicode_New
  and won’t mask leaks in PythonQt.
- Remove once CI moves off Python 3.12.

Refs: python/cpython#113190, python/cpython#113601

Author: jcfr

.github/workflows/build.yml

@@ -85,6 +85,14 @@ jobs:
 
     - name: Run cleanup tests with sanitizers
       run: |
+        # CPython 3.12 only: suppress its known interned-unicode leak that
+        # shows up as allocations via PyUnicode_New (python/cpython#113190).
+        # Fixed in 3.13 (python/cpython#113601), so we scope this to 3.12.
+        PYVER=$(python3 -c 'import sys; print(".".join(map(str, sys.version_info[:2])))')
+        if [[ "$PYVER" == "3.12" ]]; then
+          echo "leak:PyUnicode_New" >> $PWD/lsan.supp
+          export LSAN_OPTIONS="suppressions=$PWD/lsan.supp"
+        fi
         PYTHONDEVMODE=1 PYTHONASYNCIODEBUG=1 PYTHONWARNINGS=error PYTHONMALLOC=malloc_debug \
         UBSAN_OPTIONS="halt_on_error=1" ASAN_OPTIONS="detect_leaks=1:detect_stack_use_after_return=1:fast_unwind_on_malloc=0" \
         PYTHONQT_RUN_ONLY_CLEANUP_TESTS=1 \