feat: Add max-parallel Support for Gitea Actions (#36357)

Add support for `strategy.max-parallel` on Gitea Actions matrix jobs.

**How it works**
Jobs over the limit are inserted as `Blocked` instead of `Waiting`, so
runners never see them. When a job finishes, the job-status resolver
promotes one `Blocked` job per freed slot, in job order. Slots are
counted per `JobID` and scoped by reusable-workflow caller. A
`Cancelling` job still owns its runner, so it keeps its slot.

The cap is applied wherever a job can become `Waiting`: initial insert,
rerun, approval, and resolver promotion.

Best effort, not a hard invariant: two concurrent emitter passes can
each promote into the last slot, overshooting by one. It does not
compound, since every later pass recounts.

**Parsing**
Any YAML number, cast to an int as GitHub does (`1.5` → 1). `0` or
negative means unlimited. Expressions (`${{ ... }}`) are not evaluated
yet and fall back to unlimited.

**Migration**
Adds the `max_parallel` column on `action_run_job`. No index or
constraint changes.

**Compatibility**
Existing rows default to `0`, so behaviour is unchanged. No runner
changes needed: the runner protocol is untouched, and since the server
splits the matrix each runner still receives a single job.

Closes https://github.com/go-gitea/gitea/issues/35561
Signed-off-by: Pascal Zimmermann <pascal.zimmermann@theiotstudio.com>
Signed-off-by: ZPascal <pascal.zimmermann@theiotstudio.com>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

services/actions/reusable_workflow.go

@@ -354,6 +354,7 @@ func insertCallerChildren(ctx context.Context, run *actions_model.ActionRun, att
 			Needs:                   needs,
 			RunsOn:                  parsedChild.RunsOn(),
 			ContinueOnError:         parsedChild.GetContinueOnError(),
+			MaxParallel:             parseMaxParallel(jobID, parsedChild.Strategy.MaxParallelString),
 			Status:                  actions_model.StatusBlocked,
 			ParentJobID:             caller.ID,
 			WorkflowSourceRepoID:    sourceRepoID,