run_context: add GITHUB_RUN_ATTEMPT (#2458)

* run_context: add GITHUB_RUN_ATTEMPT

Fixes https://github.com/nektos/act/issues/2451
Fixes https://github.com/nektos/act/issues/1615

* fix whitespace

* fix githubcontext

* fix TestSetupEnv

---------

Co-authored-by: ChristopherHX <christopher.homberger@web.de>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/model/github_context.go

@@ -13,6 +13,7 @@ type GithubContext struct {
 	Event            map[string]interface{} `json:"event"`
 	EventPath        string                 `json:"event_path"`
 	Workflow         string                 `json:"workflow"`
+	RunAttempt       string                 `json:"run_attempt"`
 	RunID            string                 `json:"run_id"`
 	RunNumber        string                 `json:"run_number"`
 	Actor            string                 `json:"actor"`