Follow upstream support for variables (#66)

Because the upstream [PR](https://github.com/nektos/act/pull/1833) already supports variables, so this PR revert #43 (commit de529139af), and cherry-pick commit [6ce45e3](6ce45e3f24).

Co-authored-by: Kuan Yong <wong0514@gmail.com>
Reviewed-on: https://gitea.com/gitea/act/pulls/66
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: sillyguodong <gedong_1994@163.com>
Co-committed-by: sillyguodong <gedong_1994@163.com>

cmd/input.go

@@ -16,6 +16,7 @@ type Input struct {
 	reuseContainers                    bool
 	bindWorkdir                        bool
 	secrets                            []string
+	vars                               []string
 	envs                               []string
 	inputs                             []string
 	platforms                          []string
@@ -26,6 +27,7 @@ type Input struct {
 	envfile                            string
 	inputfile                          string
 	secretfile                         string
+	varfile                            string
 	insecureSecrets                    bool
 	defaultBranch                      string
 	privileged                         bool
@@ -78,6 +80,10 @@ func (i *Input) Secretfile() string {
 	return i.resolve(i.secretfile)
 }
 
+func (i *Input) Varfile() string {
+	return i.resolve(i.varfile)
+}
+
 // Workdir returns path to workdir
 func (i *Input) Workdir() string {
 	return i.resolve(".")