Add suppression for race seen in CI

.github/workflows/ci.yaml

@@ -542,6 +542,12 @@ jobs:
 
     - name: build and install
       run: |
+        # these two steps can be removed when
+        # https://github.com/nascheme/cpython_sanity/issues/12 and the images
+        # are rebuilt
+        apt update
+        apt install -y llvm
+
         python -m pip install setuptools pytest pytest-run-parallel
         CFLAGS="-g -O3 -fsanitize=thread" python -m pip install -v .
 

suppressions_free_threading.txt

@@ -50,3 +50,6 @@ race_top:set_tp_bases
 race_top:type_set_bases_unlocked
 
 race:partial_vectorcall_fallback
+
+# gh-113956: races from simultaneously interning a string
+race_top:_Py_SetImmortalUntracked