Apply ruff/flake8-pytest-style rule PT017

PT017 Found assertion on exception in `except` block, use `pytest.raises()` instead

Author: DimitriPapadopoulos

xarray/tests/test_backends.py

@@ -2072,10 +2072,8 @@ def test_unsorted_index_raises(self) -> None:
             ds2 = ondisk.isel(dim1=inds)
             # Older versions of NetCDF4 raise an exception here, and if so we
             # want to ensure we improve (that is, replace) the error message
-            try:
+            with pytest.raises(IndexError, match="first by calling .load"):
                 _ = ds2.randovar.values
-            except IndexError as err:
-                assert "first by calling .load" in str(err)
 
     def test_setncattr_string(self) -> None:
         list_of_strings = ["list", "of", "strings"]

xarray/tests/test_dask.py

@@ -255,14 +255,10 @@ def test_concat(self):
 
     def test_missing_methods(self):
         v = self.lazy_var
-        try:
+        with pytest.raises(NotImplementedError, match="dask"):
             v.argsort()
-        except NotImplementedError as err:
-            assert "dask" in str(err)
-        try:
+        with pytest.raises(NotImplementedError, match="dask"):
             v[0].item()
-        except NotImplementedError as err:
-            assert "dask" in str(err)
 
     def test_univariate_ufunc(self):
         u = self.eager_var