Full error text:
fatal: unable to access 'https://github.com/Repository_name': schannel: failed to open CA file 'C:/Users/Username/AppData/Local/GitHubDesktop/app-1.2.1/resources/app/git/mingw64/ssl/certs/ca-bundle.crt': No such process
Application just stopped to work and throwing this error every time when I try to fetch, pull, push or clone any repository. The same commands in bash work correctly
Go to %ProgramData%/Git
open config file with a text editor and substitute
sslCAInfo = ... some stuff
with
sslCAInfo = C:/Program Files/Git/mingw64/ssl/certs/ca-bundle.crt
This has been already discussed in this issue on Github https://github.com/desktop/desktop/issues/4817 and it will be fixed asap.