PHPStan: added baseline

GA: build.yml - PHPStan - updated PHP versions

Fixed PHPStan errors

GitRepository: method run() is public now (#100)

Git: isRemoteUrlReadable() - returns TRUE for empty repositories

Closes #92

Runners: added OldGitRunner

#82
#86

GitRepository: pull(), push() & fetch() - accepts string[] in $remote

#77 (comment)

GitRepository: checkout - removed '--end-of-options' (closes #77)

Uses --end-of-options after command options (for security reasons)

GitRepository: fixed parameters in `git log` commands (closes #70)