[doc] Fix padding in timeit (GH-22152)

Compare -p and -u options help in rendered output to see the difference.
(cherry picked from commit 594f0ce)

Co-authored-by: Andre Delfino <[email protected]>

Author: miss-islington

Doc/library/timeit.rst

@@ -233,7 +233,7 @@ Where the following options are understood:
 
 .. cmdoption:: -u, --unit=U
 
-    specify a time unit for timer output; can select nsec, usec, msec, or sec
+   specify a time unit for timer output; can select nsec, usec, msec, or sec
 
    .. versionadded:: 3.5