[query] MT.tail should prefer n_rows to n.

CHANGELOG: The `n` parameter of `MatrixTable.tail` is deprecated in favor of a new `n_rows` parameter.

MT.head already does this.

hail/python/hail/matrixtable.py

@@ -4047,8 +4047,8 @@ def head(self, n_rows: Optional[int], n_cols: Optional[int] = None, *, n: Option
             mt = MatrixTable(ir.MatrixColsHead(mt._mir, n_cols))
         return mt
 
-    @typecheck_method(n=nullable(int), n_cols=nullable(int))
-    def tail(self, n: Optional[int], n_cols: Optional[int] = None) -> 'MatrixTable':
+    @typecheck_method(n_rows=nullable(int), n_cols=nullable(int), n=nullable(int))
+    def tail(self, n_rows: Optional[int], n_cols: Optional[int] = None, *, n: Optional[int] = None) -> 'MatrixTable':
         """Subset matrix to last `n` rows.
 
         Examples
@@ -4087,20 +4087,31 @@ def tail(self, n: Optional[int], n_cols: Optional[int] = None) -> 'MatrixTable':
 
         Parameters
         ----------
-        n : :obj:`int`
+        n_rows : :obj:`int`
             Number of rows to include (all rows included if ``None``).
         n_cols : :obj:`int`, optional
             Number of cols to include (all cols included if ``None``).
+        n : :obj:`int`
+            Deprecated in favor of n_rows.
 
         Returns
         -------
         :class:`.MatrixTable`
             Matrix including the last `n` rows and last `n_cols` cols.
         """
+        if n_rows is not None and n is not None:
+            raise ValueError('Both n and n_rows specified. Only one may be specified.')
+
+        if n_rows is not None:
+            n_rows_name = 'n_rows'
+        else:
+            n_rows = n
+            n_rows_name = 'n'
+
         mt = self
         if n is not None:
             if n < 0:
-                raise ValueError(f"MatrixTable.tail: expect 'n' to be non-negative or None, found '{n}'")
+                raise ValueError(f"MatrixTable.tail: expect '{n_rows_name}' to be non-negative or None, found '{n}'")
             mt = MatrixTable(ir.MatrixRowsTail(mt._mir, n))
         if n_cols is not None:
             if n_cols < 0: