[SPARK-48823][DOCS] Improve clarity in lag docstring

### What changes were proposed in this pull request?
This PR edits grammar in `pyspark.sql.functions.lag` docstring.

### Why are the changes needed?
To improve the documentation.

### Does this PR introduce any user-facing change?
No changes in behavior are introduced.

### How was this patch tested?
Existing tests.

### Was this patch authored or co-authored using generative AI tooling?
No

Closes apache#47236 from thomhart31/docs-lag.

Lead-authored-by: thomas.hart <thomas.hart@databricks.com>
Co-authored-by: Kent Yao <yao@apache.org>
Signed-off-by: Kent Yao <yao@apache.org>

python/pyspark/sql/functions/builtin.py

@@ -7305,36 +7305,36 @@ def lag(col: "ColumnOrName", offset: int = 1, default: Optional[Any] = None) ->
     |  b|  2|
     +---+---+
     >>> w = Window.partitionBy("c1").orderBy("c2")
-    >>> df.withColumn("previos_value", lag("c2").over(w)).show()
-    +---+---+-------------+
-    | c1| c2|previos_value|
-    +---+---+-------------+
-    |  a|  1|         NULL|
-    |  a|  2|            1|
-    |  a|  3|            2|
-    |  b|  2|         NULL|
-    |  b|  8|            2|
-    +---+---+-------------+
-    >>> df.withColumn("previos_value", lag("c2", 1, 0).over(w)).show()
-    +---+---+-------------+
-    | c1| c2|previos_value|
-    +---+---+-------------+
-    |  a|  1|            0|
-    |  a|  2|            1|
-    |  a|  3|            2|
-    |  b|  2|            0|
-    |  b|  8|            2|
-    +---+---+-------------+
-    >>> df.withColumn("previos_value", lag("c2", 2, -1).over(w)).show()
-    +---+---+-------------+
-    | c1| c2|previos_value|
-    +---+---+-------------+
-    |  a|  1|           -1|
-    |  a|  2|           -1|
-    |  a|  3|            1|
-    |  b|  2|           -1|
-    |  b|  8|           -1|
-    +---+---+-------------+
+    >>> df.withColumn("previous_value", lag("c2").over(w)).show()
+    +---+---+--------------+
+    | c1| c2|previous_value|
+    +---+---+--------------+
+    |  a|  1|          NULL|
+    |  a|  2|             1|
+    |  a|  3|             2|
+    |  b|  2|          NULL|
+    |  b|  8|             2|
+    +---+---+--------------+
+    >>> df.withColumn("previous_value", lag("c2", 1, 0).over(w)).show()
+    +---+---+--------------+
+    | c1| c2|previous_value|
+    +---+---+--------------+
+    |  a|  1|             0|
+    |  a|  2|             1|
+    |  a|  3|             2|
+    |  b|  2|             0|
+    |  b|  8|             2|
+    +---+---+--------------+
+    >>> df.withColumn("previous_value", lag("c2", 2, -1).over(w)).show()
+    +---+---+--------------+
+    | c1| c2|previous_value|
+    +---+---+--------------+
+    |  a|  1|            -1|
+    |  a|  2|            -1|
+    |  a|  3|             1|
+    |  b|  2|            -1|
+    |  b|  8|            -1|
+    +---+---+--------------+
     """
     from pyspark.sql.classic.column import _to_java_column