BUG: fix duplicate entries in LaTeX List of Tables when using longtable environments
- [x] closes #34360
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

this should target 1.2 as there was a large refactor in this code (which u already did), just move the note  @ivanovmg if you'd have a look. > @ivanovmg if you'd have a look.

@jreback, this looks good to me. However, if there are other modifications to longtable in future, we may want to redefine the method ``get_result`` for ``LongTableBuilder``, where we specify more specific order of the items. Note that this PR suggests to include header in the middle separator. This is not very obvious for the reader. But the author left the comment why it is there, so it is OK for now. lgtm ping on green. thanks @jeschwar 