perf(actions): index action_run.commit_sha (#39559)

The API filter `head_sha` on `GET /repos/{owner}/{repo}/actions/runs`
selects runs by `commit_sha`, so `commit_sha` needs an index. For a
action_run table with 212k rows:

- Without the index: the query read 212k rows, and the API request took
35-52 s.
- With the index: the query read 94 rows in 0.14 s, and the API request
took 2-4 s.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/actions/run.go

@@ -39,9 +39,9 @@ type ActionRun struct {
 	TriggerUserID     int64                  `xorm:"index"`
 	TriggerUser       *user_model.User       `xorm:"-"`
 	ScheduleID        int64
-	Ref               string `xorm:"index"` // the commit/tag/… that caused the run
-	IsRefDeleted      bool   `xorm:"-"`
-	CommitSHA         string
+	Ref               string                       `xorm:"index"` // the commit/tag/… that caused the run
+	IsRefDeleted      bool                         `xorm:"-"`
+	CommitSHA         string                       `xorm:"index"`
 	IsForkPullRequest bool                         // If this is triggered by a PR from a forked repository or an untrusted user, we need to check if it is approved and limit permissions when running the workflow.
 	NeedApproval      bool                         // may need approval if it's a fork pull request
 	ApprovedBy        int64                        `xorm:"index"` // who approved