Fix not being able to delete bypass_actors

This is a quirk upstream, where they introduced a new function
`UpdateRulesetNoBypassActor` to work around the issue of
`UpdateRuleset` not deleting BypassActors when there's an empty array.
google/go-github#3174

Not sure why they decided to introduce a new function instead of just
patching the original. Compatibility issues?
Is there ever a use case where we need to keep BypassActors around
when the non-empty list becomes an empty list?

github/resource_github_repository_ruleset.go

@@ -540,7 +540,7 @@ func resourceGithubRepositoryRulesetUpdate(d *schema.ResourceData, meta interfac
 
 	ctx := context.WithValue(context.Background(), ctxId, rulesetID)
 
-	ruleset, _, err := client.Repositories.UpdateRuleset(ctx, owner, repoName, rulesetID, rulesetReq)
+	ruleset, _, err := client.Repositories.UpdateRulesetNoBypassActor(ctx, owner, repoName, rulesetID, rulesetReq)
 	if err != nil {
 		return err
 	}

github/respository_rules_utils.go

@@ -35,9 +35,6 @@ func resourceGithubRulesetObject(d *schema.ResourceData, org string) *github.Rul
 }
 
 func expandBypassActors(input []interface{}) []*github.BypassActor {
-	if len(input) == 0 {
-		return nil
-	}
 	bypassActors := make([]*github.BypassActor, 0)
 
 	for _, v := range input {