[3.12] gh-107432 Fix incorrect indentation in annotations HOWTO (GH-107445) (#107654)

gh-107432 Fix incorrect indentation in annotations HOWTO (GH-107445)

gh-107432 Fix incorrect indentation in annotations document

Body text in https://docs.python.org/3/howto/annotations.html was
indented throughout, and was being rendered in blockquote elements.
(cherry picked from commit 5e2746d6e2fb0da29225ead7135f078c5f087b57)

Co-authored-by: Daniele Procida <daniele@vurt.org>