[3.14] Docs: fix missing period in Doc/library/stdtypes.rst (GH-145935) (#145936)

Docs: fix missing period in `Doc/library/stdtypes.rst` (GH-145935)
(cherry picked from commit 51e8acf)

Co-authored-by: Connor Gibson <connor@nextdoortech.net>

Author: miss-islington

Doc/library/stdtypes.rst

@@ -1286,7 +1286,7 @@ Mutable sequence types also support the following methods:
    :no-typesetting:
 .. method:: sequence.append(value, /)
 
-   Append *value* to the end of the sequence
+   Append *value* to the end of the sequence.
    This is equivalent to writing ``seq[len(seq):len(seq)] = [value]``.
 
 .. method:: bytearray.clear()