MNT: prepare h5netcdf backend for (coming) change in dimension handli…

…ng (#6200)

* prepare h5netcdf backend for (coming) change in dimension handling

* [test-upstream]

xarray/backends/h5netcdf_.py

@@ -81,7 +81,11 @@ def _read_attributes(h5netcdf_var):
 
 
 _extract_h5nc_encoding = functools.partial(
-    _extract_nc4_variable_encoding, lsd_okay=False, h5py_okay=True, backend="h5netcdf"
+    _extract_nc4_variable_encoding,
+    lsd_okay=False,
+    h5py_okay=True,
+    backend="h5netcdf",
+    unlimited_dims=None,
 )
 
 
@@ -231,12 +235,24 @@ def get_attrs(self):
         return FrozenDict(_read_attributes(self.ds))
 
     def get_dimensions(self):
-        return self.ds.dimensions
+        if Version(h5netcdf.__version__) >= Version("0.14.0.dev0"):
+            return FrozenDict((k, len(v)) for k, v in self.ds.dimensions.items())
+        else:
+            return self.ds.dimensions
 
     def get_encoding(self):
-        return {
-            "unlimited_dims": {k for k, v in self.ds.dimensions.items() if v is None}
-        }
+        if Version(h5netcdf.__version__) >= Version("0.14.0.dev0"):
+            return {
+                "unlimited_dims": {
+                    k for k, v in self.ds.dimensions.items() if v.isunlimited()
+                }
+            }
+        else:
+            return {
+                "unlimited_dims": {
+                    k for k, v in self.ds.dimensions.items() if v is None
+                }
+            }
 
     def set_dimension(self, name, length, is_unlimited=False):
         if is_unlimited: