Set the default branch inside the event data (#354)

* set ${{github.event.repository.default_branch}}

* change `ok == false` to `!ok`

Co-authored-by: Casey Lee <cplee@nektos.com>

act/runner/runner.go

@@ -22,6 +22,7 @@ type Config struct {
 	BindWorkdir     bool              // bind the workdir to the job container
 	EventName       string            // name of event to run
 	EventPath       string            // path to JSON file to use for event.json in containers
+	DefaultBranch   string            // name of the main branch for this repository
 	ReuseContainers bool              // reuse containers to maintain state
 	ForcePull       bool              // force pulling of the image, if already present
 	LogOutput       bool              // log the output from docker run