chore: Unbreak doctest CI

[neilconway]

File was renamed and split into smaller files as part of #20183.

Rationale for this change

CI is failing with:

   Doc-tests datafusion
error: couldn't read `datafusion/core/src/../../../docs/source/library-user-guide/upgrading.md`: No such file or directory (os error 2)
    --> datafusion/core/src/lib.rs:1182:1
     |
1182 | / doc_comment::doctest!(
1183 | |     "../../../docs/source/library-user-guide/upgrading.md",
1184 | |     library_user_guide_upgrading
1185 | | );
     | |_^
     |
     = note: this error originates in the macro `include_str` which comes from the expansion of the macro `doc_comment::doctest` (in Nightly builds, run with -Z macro-backtrace for more info)

What changes are included in this PR?

[neilconway]

Note that there are still various references to a file called upgrading.md in the source tree; I haven't attempted to fix all those as part of this PR.

$ ag upgrading.md | wc -l
      31

[neilconway]

PTAL @avantgardnerio @alamb

[Jefffrey]

Thanks @neilconway, merged to unbreak CI

Note that there are still various references to a file called upgrading.md in the source tree; I haven't attempted to fix all those as part of this PR.

This would be good to address in a followup 👍