ci: lint with uncrustify #18563

This lint job will ensure that the C codebase is properly formatted at
all times. This helps eliminate most of clint.py.

To save CI time, it's faster to manually compile uncrustify and cache
the binary instead of using homebrew (the apt-get package is too old).

src/nvim/math.c

@@ -1,7 +1,9 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
+// uncrustify:off
 #include <math.h>
+// uncrustify:on
 #include <stdint.h>
 #include <string.h>