Resolve warnings from running tests

* [ ] ```/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum.py:873: DeprecationWarning: The method the [] operator will change behaviour in the future. It will then return a plain numpy vector. You are advised to change to use the numpy_vector() method right away
warnings.warn(```

* [ ] ```python/tests/rd_tests/test_rd_sum_vector.py: 1 warning
python/tests/rd_tests/test_sum.py: 7 warnings
python/tests/rd_tests/test_sum_equinor.py: 3 warnings
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum.py:407: DeprecationWarning: The method get_vector() has been deprecated, use numpy_vector() instead
warnings.warn(```

* [ ] ```python/tests/rd_tests/test_sum.py::SumTest::test_first_last
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum.py:458: DeprecationWarning: The method get_values() has been deprecated - use numpy_vector() instead.
warnings.warn(```
* [ ] ```python/tests/rd_tests/test_sum.py::SumTest::test_resample_extrapolate
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum.py:799: DeprecationWarning: The function get_last_value() is deprecated, use last_value() instead
warnings.warn(```

* [ ] ```python/tests/rd_tests/test_sum.py::SumTest::test_vector
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum_vector.py:29: DeprecationWarning: The report_only flag to the SummaryVector will be removed
warnings.warn(```

* [ ] ```python/tests/rd_tests/test_sum.py: 115 warnings
python/tests/rd_tests/test_sum_equinor.py: 1 warning
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum_vector.py:98: DeprecationWarning: The mpl_dates property has been deprecated - use numpy_dates instead
warnings.warn```

* [ ] ```python/tests/rd_tests/test_sum.py: 115 warnings
python/tests/rd_tests/test_sum_equinor.py: 2 warnings
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum.py:1281: DeprecationWarning: The get_mpl_dates( ) method has been deprecated - use numpy_dates instead
warnings.warn(```

* [ ] ```python/tests/rd_tests/test_sum_equinor.py::SumTest::test_dates
/prog/res/komodo/bleeding-py38-rhel7/root/lib64/python3.8/site-packages/resdata/summary/rd_sum.py:1265: DeprecationWarning: The mpl_dates property has been deprecated - use numpy_dates instead
warnings.warn(```