Backport PR #44658 on branch 1.3.x (BUG: groupby.sum with timedelta64 and NaT)
Backport PR #44658
```
=========================== short test summary info ============================
FAILED pandas/tests/frame/methods/test_rename.py::TestRename::test_rename_inplace
= 1 failed, 169202 passed, 6163 skipped, 962 xfailed, 3 xpassed, 4 warnings in 2144.77s (0:35:44) =
```

is a known flaky test