Fix URL in FutureWarning for .loc[list-of-labels] with missing labels
- [X] closes #19143
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`


Do you know if sphinx let's you have multiple labels for the same header? It'd be nice to add a 

    .. deprecate_loc_reindex_listlike

in the same spot, so that both URLs point to the same spot.
 >Do you know if sphinx let's you have multiple labels for the same header?

Yeah, was wondering that myself since it seems like it'd be a nicer solution to just make the URL work than to change it.  Had to try a few variations, but eventually got the second label working, at least for my local build of the docs.

No real point in changing to URL in this case; I'll make it https but leave everything else as is.  Assuming this is fine, will check the docs generated by travis after this gets merged to make sure it's working there too.
   thanks!