MacOS Catalina apparently ships a stripped down svn that doesn't have
`svnversion`, which we use to print the revision.
For now skip the entire step to remove error spam.
Fixes#6267.
[ci skip]
This runs build_tools/style.fish, which runs clang-format on C++, fish_indent on fish and (new) black on python.
If anything is wrong with the formatting, we should fix the tools, but automated formatting is worth it.
