Make runs-on support variable expression (#91)

Partial implementation of https://gitea.com/gitea/act_runner/issues/445, the Gitea side also needs a PR for the entire functionality.
Gitea side: https://github.com/go-gitea/gitea/pull/29468

Co-authored-by: Jason Song <i@wolfogre.com>
Reviewed-on: https://gitea.com/gitea/act/pulls/91
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: sillyguodong <gedong_1994@163.com>
Co-committed-by: sillyguodong <gedong_1994@163.com>

pkg/jobparser/interpeter.go

@@ -15,6 +15,7 @@ func NewInterpeter(
 	matrix map[string]interface{},
 	gitCtx *model.GithubContext,
 	results map[string]*JobResult,
+	vars map[string]string,
 ) exprparser.Interpreter {
 	strategy := make(map[string]interface{})
 	if job.Strategy != nil {
@@ -62,6 +63,7 @@ func NewInterpeter(
 		Matrix:   matrix,
 		Needs:    using,
 		Inputs:   nil, // not supported yet
+		Vars:     vars,
 	}
 
 	config := exprparser.Config{