Correct doc for axvline arg x which sets x not y

Fixes matplotlib#29606

Author: gdmcbain

lib/matplotlib/axes/_axes.py

@@ -818,7 +818,7 @@ def axvline(self, x=0, ymin=0, ymax=1, **kwargs):
         Parameters
         ----------
         x : float, default: 0
-            y position in :ref:`data coordinates <coordinate-systems>`.
+            x position in :ref:`data coordinates <coordinate-systems>`.
 
         ymin : float, default: 0
             The start y-position in :ref:`axes coordinates <coordinate-systems>`.