altering rename_cmip6 to retain coord info instead of dropping (#345)

* altering rename_cmip6 to retain coord info instead of dropping

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

xmip/preprocessing.py

@@ -75,7 +75,8 @@ def _maybe_rename_dims(da, rdict):
                 if di in candidates:
                     da = da.swap_dims({di: target})
                     if di in da.coords:
-                        da = da.drop_vars(di)
+                        if not di == target:
+                            da = da.rename({di: target}).set_xindex(target)
         return da
 
     # first take care of the dims and reconstruct a clean ds