Update compat error checking to disallow "minimal" in concat() (#9525)

* update compat error checking

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

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---------

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

Author: VeckoTheGecko

xarray/core/concat.py

@@ -255,7 +255,7 @@ def concat(
     except StopIteration as err:
         raise ValueError("must supply at least one object to concatenate") from err
 
-    if compat not in _VALID_COMPAT:
+    if compat not in set(_VALID_COMPAT) - {"minimal"}:
         raise ValueError(
             f"compat={compat!r} invalid: must be 'broadcast_equals', 'equals', 'identical', 'no_conflicts' or 'override'"
         )

xarray/tests/test_concat.py

@@ -663,6 +663,9 @@ def test_concat_errors(self):
         with pytest.raises(ValueError, match=r"compat.* invalid"):
             concat(split_data, "dim1", compat="foobar")
 
+        with pytest.raises(ValueError, match=r"compat.* invalid"):
+            concat(split_data, "dim1", compat="minimal")
+
         with pytest.raises(ValueError, match=r"unexpected value for"):
             concat([data, data], "new_dim", coords="foobar")