feat: don't require docker (#16)

The only reason docker is really required by now, is that act_runner ping docker.
This change only pings docker if a label with `docker://` is added to the runner.

Plain labels without `:` like `self-hosted` are run directly on the system. Previously the pseudo non docker label `-self-hosted` have been required like this `self-hosted:docker://-self-hosted`, but due to docker ping this still required a dockerd to be pingable.

Co-authored-by: Christopher Homberger <[email protected]>
Reviewed-on: https://gitea.com/gitea/act_runner/pulls/16
Reviewed-by: Jason Song <[email protected]>
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: ChristopherHX <[email protected]>
Co-committed-by: ChristopherHX <[email protected]>

cmd/register_test.go

@@ -3,7 +3,7 @@ package cmd
 import "testing"
 
 func TestValidateLabels(t *testing.T) {
-	labels := []string{"ubuntu-latest:docker://node:16-buster"}
+	labels := []string{"ubuntu-latest:docker://node:16-buster", "self-hosted"}
 	if err := validateLabels(labels); err != nil {
 		t.Errorf("validateLabels() error = %v", err)
 	}