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

Signed-off-by: Christian Heimes <christian@python.org>
diff --git a/Modules/_sha3/sha3module.c b/Modules/_sha3/sha3module.c
index 27f6938..aba7f6d 100644
--- a/Modules/_sha3/sha3module.c
+++ b/Modules/_sha3/sha3module.c
@@ -525,7 +525,7 @@ static PyGetSetDef SHA3_getseters[] = {
     static PyType_Spec type_spec_obj = { \
         .name = "_sha3." type_name, \
         .basicsize = sizeof(SHA3object), \
-        .flags = Py_TPFLAGS_DEFAULT, \
+        .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE, \
         .slots = type_slots \
     }