fix: resolve YAML anchors and aliases in Actions workflows (#38984)

Workflows using YAML anchors are rejected as invalid, because a workflow
is split into one document per job and an alias whose anchor lands in
another job's document no longer resolves.

Aliases are now expanded once, right after the workflow is parsed and
before anything reads or splits it, bounded like GitHub's parser so
nested aliases cannot expand without limit. Merge keys stay unsupported,
as they are upstream.

Fixes https://github.com/go-gitea/gitea/issues/38983
Signed-off-by: silverwind <me@silverwind.io>

routers/web/repo/actions/actions.go

@@ -4,7 +4,6 @@
 package actions
 
 import (
-	"bytes"
 	stdCtx "context"
 	"errors"
 	"fmt"
@@ -21,6 +20,7 @@ import (
 	repo_model "gitea.dev/models/repo"
 	"gitea.dev/models/unit"
 	"gitea.dev/modules/actions"
+	"gitea.dev/modules/actions/jobparser"
 	"gitea.dev/modules/base"
 	"gitea.dev/modules/container"
 	"gitea.dev/modules/git"
@@ -220,7 +220,7 @@ func prepareWorkflowTemplate(ctx *context.Context, commit *git.Commit) (workflow
 			ctx.ServerError("GetContentFromEntry", err)
 			return nil, ""
 		}
-		wf, err := act_model.ReadWorkflow(bytes.NewReader(content))
+		wf, err := jobparser.ReadWorkflow(content)
 		if err != nil {
 			workflow.ErrMsg = ctx.Locale.TrString("actions.runs.invalid_workflow_helper", err.Error())
 			workflows = append(workflows, workflow)
@@ -390,7 +390,7 @@ func loadScopedWorkflowModel(ctx *context.Context, repo *repo_model.Repository,
 	if content == nil {
 		return nil // the workflow does not exist on the source's default branch
 	}
-	wf, err := act_model.ReadWorkflow(bytes.NewReader(content))
+	wf, err := jobparser.ReadWorkflow(content)
 	if err != nil {
 		return nil
 	}