Fix dtype coding test failures

Author: spencerkclark

xarray/coding/times.py

@@ -1355,20 +1355,15 @@ def encode(self, variable: Variable, name: T_Name = None) -> Variable:
 
             units = encoding.pop("units", None)
             calendar = encoding.pop("calendar", None)
-            dtype = encoding.pop("dtype", None)
+            dtype = encoding.get("dtype", None)
 
             # in the case of packed data we need to encode into
             # float first, the correct dtype will be established
             # via CFScaleOffsetCoder/CFMaskCoder
-            set_dtype_encoding = None
             if "add_offset" in encoding or "scale_factor" in encoding:
-                set_dtype_encoding = dtype
                 dtype = data.dtype if data.dtype.kind == "f" else "float64"
             (data, units, calendar) = encode_cf_datetime(data, units, calendar, dtype)
 
-            # retain dtype for packed data
-            if set_dtype_encoding is not None:
-                safe_setitem(encoding, "dtype", set_dtype_encoding, name=name)
             safe_setitem(attrs, "units", units, name=name)
             safe_setitem(attrs, "calendar", calendar, name=name)
 
@@ -1420,22 +1415,16 @@ def encode(self, variable: Variable, name: T_Name = None) -> Variable:
         if np.issubdtype(variable.data.dtype, np.timedelta64):
             dims, data, attrs, encoding = unpack_for_encoding(variable)
 
-            dtype = encoding.pop("dtype", None)
+            dtype = encoding.get("dtype", None)
 
             # in the case of packed data we need to encode into
             # float first, the correct dtype will be established
             # via CFScaleOffsetCoder/CFMaskCoder
-            set_dtype_encoding = None
             if "add_offset" in encoding or "scale_factor" in encoding:
-                set_dtype_encoding = dtype
                 dtype = data.dtype if data.dtype.kind == "f" else "float64"
 
             data, units = encode_cf_timedelta(data, encoding.pop("units", None), dtype)
 
-            # retain dtype for packed data
-            if set_dtype_encoding is not None:
-                safe_setitem(encoding, "dtype", set_dtype_encoding, name=name)
-
             safe_setitem(attrs, "units", units, name=name)
 
             return Variable(dims, data, attrs, encoding, fastpath=True)