[MINOR][DOCS][PYTHON][PS] Fix the .groupby() method docstring

### What changes were proposed in this pull request?

Update the docstring for the `.groupby()` method.

### Why are the changes needed?

The `.groupby()` method accept a list of columns (or a single column), and a column is defined by a `Series` or name (`Label`). It's a bit confusing to say "using a Series of columns", because `Series` (capitalized) is a specific object that isn't actually used/reasonable to use here.

### Does this PR introduce _any_ user-facing change?

Yes (documentation)

### How was this patch tested?

N/A

Closes #38625 from deepyaman/patch-3.

Authored-by: Deepyaman Datta <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>
(cherry picked from commit 71154dc)
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: deepyaman

python/pyspark/pandas/generic.py

@@ -2190,7 +2190,7 @@ def groupby(
         dropna: bool = True,
     ) -> "GroupBy[FrameLike]":
         """
-        Group DataFrame or Series using a Series of columns.
+        Group DataFrame or Series using one or more columns.
 
         A groupby operation involves some combination of splitting the
         object, applying a function, and combining the results. This can be