Fix sdba Grouper.get_coordinate after xarray update (#2038)

<!--Please ensure the PR fulfills the following requirements! -->
<!-- If this is your first PR, make sure to add your details to the
AUTHORS.rst! -->
### Pull Request Checklist:
- [x] This PR addresses an already opened issue (for bug fixes /
features)
    - This PR fixes #2037 
- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] (If applicable) Documentation has been added / updated (for bug
fixes / features)
- [ ] CHANGELOG.rst has been updated (with summary of main changes)
- [ ] Link to issue (:issue:`number`) and pull request (:pull:`number`)
has been added

### What kind of change does this PR introduce?

* Uses a dumber way of getting the max doy, that doesn't rely on a
private xarray function. There is a public xarray function in >=2024.09,
but we still support >=2023.11.

### Does this PR introduce a breaking change?
Yes, only if a non-uniform calendar was used with a subset of years that
did not include a leap year. The max doy is now static (`standard =>
366`, for example) and not dynamic (`standard, 2004 => 366`).

src/xclim/sdba/base.py

@@ -15,7 +15,7 @@
 import xarray as xr
 from boltons.funcutils import wraps
 
-from xclim.core.calendar import get_calendar
+from xclim.core.calendar import get_calendar, max_doy
 from xclim.core.options import OPTIONS, SDBA_ENCODE_CF
 from xclim.core.utils import uses_dask
 
@@ -195,10 +195,8 @@ def get_coordinate(self, ds: xr.Dataset | None = None) -> xr.DataArray:
         if self.prop == "dayofyear":
             if ds is not None:
                 cal = get_calendar(ds, dim=self.dim)
-                mdoy = max(
-                    xr.coding.calendar_ops._days_in_year(yr, cal)
-                    for yr in np.unique(ds[self.dim].dt.year)
-                )
+                # TODO : Change this to `ds[self.dim].dt.days_in_year.max().item()` when minimum xarray is 2024.09
+                mdoy = max_doy[cal]
             else:
                 mdoy = 365
             return xr.DataArray(