Avoid DeprecationWarnings (#788)

newsfragments/788.bugfix

@@ -0,0 +1 @@
+Fix ``DeprecationWarning``s raised during tests

src/dxtbx/format/nxmx_writer.py

@@ -159,7 +159,9 @@ def construct_entry(self):
         f = self.handle
         f.attrs["NX_class"] = "NXroot"
         f.attrs["file_name"] = os.path.basename(output_file_name)
-        f.attrs["file_time"] = datetime.datetime.utcnow().strftime("%Y-%m-%dT%H:%M:%SZ")
+        f.attrs["file_time"] = datetime.datetime.now(datetime.UTC).strftime(
+            "%Y-%m-%dT%H:%M:%SZ"
+        )
         f.attrs["HDF5_Version"] = h5py.version.hdf5_version
         entry = f.create_group("entry")
         entry.attrs["NX_class"] = "NXentry"

src/dxtbx/nexus/__init__.py

@@ -124,7 +124,7 @@ def read_models(self, index: int = 0):
 
         def get_wavelength(wavelength):
             if wavelength.shape in ((), (1,)):
-                wavelength_value = wavelength[()]
+                wavelength_value = wavelength[()].item()
             else:
                 wavelength_value = wavelength[index]
             wavelength_units = nxmx.units(wavelength)