Update serializer example using type hints

[94noni]

Hi, small proposition to upgrade code example here in the serializer doc using type hint on object to serialize to make example more robust from the input to output

Before continuing on this page, I want to ask if it is useful or not Thank you!

[javiereguiluz]

I like this proposal. @wouterj do you agree on adding this in 6.0 branch and up? Thanks!

[javiereguiluz]

My vote is 👍 ... but please only update this article and not all docs but that would create multiple hard-to-solve merge conflicts. Thanks!

But first, let's wait to read the opinion of @xabbuh and @OskarStark. Thanks!

[wouterj]

:+1: for 4.4 and up. This is what we have done in most other cases and will result in the least merge difficulty.

(Javier, if you want me to take care of (up-)merging this let me know)

[javiereguiluz]

Antoine, thanks for this improvement. Merged!