[3.13] Clarify base64.a85encode docs: *wrapcols* doesn't count the newline (GH-119409) (GH-119483)

Clarify base64.a85encode docs: *wrapcols* doesn't count the newline (GH-119409)
(cherry picked from commit ffa24aa)

Co-authored-by: Petr Viktorin <[email protected]>

Author: miss-islington

Doc/library/base64.rst

@@ -193,7 +193,7 @@ The modern interface provides:
 
    *wrapcol* controls whether the output should have newline (``b'\n'``)
    characters added to it. If this is non-zero, each output line will be
-   at most this many characters long.
+   at most this many characters long, excluding the trailing newline.
 
    *pad* controls whether the input is padded to a multiple of 4
    before encoding. Note that the ``btoa`` implementation always pads.

Lib/base64.py

@@ -332,7 +332,7 @@ def a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False):
 
     wrapcol controls whether the output should have newline (b'\\n') characters
     added to it. If this is non-zero, each output line will be at most this
-    many characters long.
+    many characters long, excluding the trailing newline.
 
     pad controls whether the input is padded to a multiple of 4 before
     encoding. Note that the btoa implementation always pads.