bpo-43908: Mark ssl, hash, and hmac types as immutable (GH-25792)

Signed-off-by: Christian Heimes <christian@python.org>
diff --git a/Modules/sha1module.c b/Modules/sha1module.c
index 9ac46c5..1d4bde2 100644
--- a/Modules/sha1module.c
+++ b/Modules/sha1module.c
@@ -462,7 +462,7 @@ static PyType_Slot sha1_type_slots[] = {
 static PyType_Spec sha1_type_spec = {
     .name = "_sha1.sha1",
     .basicsize =  sizeof(SHA1object),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION | Py_TPFLAGS_IMMUTABLETYPE,
     .slots = sha1_type_slots
 };