fix: support Python < 3.6

Author: henryiii

include/pybind11/gil.h

@@ -137,7 +137,9 @@ class gil_scoped_release {
         auto &internals = detail::get_internals();
         tstate = PyEval_SaveThread();
         if (disassoc) {
-            auto *key = internals.tstate;
+            // Python >= 3.7 can remove this, it's an int before 3.7
+            // NOLINTNEXTLINE(readability-qualified-auto)
+            auto key = internals.tstate;
             PYBIND11_TLS_DELETE_VALUE(key);
         }
     }
@@ -160,7 +162,9 @@ class gil_scoped_release {
             PyEval_RestoreThread(tstate);
         }
         if (disassoc) {
-            auto *key = detail::get_internals().tstate;
+            // Python >= 3.7 can remove this, it's an int before 3.7
+            // NOLINTNEXTLINE(readability-qualified-auto)
+            auto key = detail::get_internals().tstate;
             PYBIND11_TLS_REPLACE_VALUE(key, tstate);
         }
     }