Update racket to version 8.5 / rev 19 via SR 981461
https://build.opensuse.org/request/show/981461
by user WernerFink + dimstar_suse
- Add patch racket-amsmath-mathabx.patch
* Avoid conflict between modern amsmath and mathabx LaTeX styles to
get e.g. scsh build again (forwarded request 981449 from WernerFink)