feature: Add support for github action variables (#1833)

* feature: Add support for github action variables

* add --var flag for github variables

* unitests: Updated unittests to cover vars context.

* Remove syntax extension for vars and correct unit tests

* Update pkg/runner/expression.go

Co-authored-by: ChristopherHX <christopher.homberger@web.de>

---------

Co-authored-by: kuanyong-wong-partior <kuanyong.wong@partior.com>
Co-authored-by: ChristopherHX <christopher.homberger@web.de>

pkg/exprparser/interpreter.go

@@ -19,6 +19,7 @@ type EvaluationEnvironment struct {
 	Steps    map[string]*model.StepResult
 	Runner   map[string]interface{}
 	Secrets  map[string]string
+	Vars     map[string]string
 	Strategy map[string]interface{}
 	Matrix   map[string]interface{}
 	Needs    map[string]Needs
@@ -148,6 +149,7 @@ func (impl *interperterImpl) evaluateNode(exprNode actionlint.ExprNode) (interfa
 	}
 }
 
+// nolint:gocyclo
 func (impl *interperterImpl) evaluateVariable(variableNode *actionlint.VariableNode) (interface{}, error) {
 	switch strings.ToLower(variableNode.Name) {
 	case "github":
@@ -167,6 +169,8 @@ func (impl *interperterImpl) evaluateVariable(variableNode *actionlint.VariableN
 		return impl.env.Runner, nil
 	case "secrets":
 		return impl.env.Secrets, nil
+	case "vars":
+		return impl.env.Vars, nil
 	case "strategy":
 		return impl.env.Strategy, nil
 	case "matrix":