internal/task: order doc/next removal after api/next promotion

The TestCheckAPIFragments test in cmd/relnote looks at api/next content
and requires doc/next to have corresponding entries. So, make sure that
test is happy by starting to remove doc/next no sooner than api/next is
promoted.

We ran into this in CL 634057.

For golang/go#70655.

Change-Id: Ic4d23c00507f057daa0de2a38ef5e83150d6c0c4
Reviewed-on: https://go-review.googlesource.com/c/build/+/634044
Auto-Submit: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: dmitshur

internal/relui/workflows.go

@@ -314,7 +314,8 @@ func RegisterReleaseWorkflows(ctx context.Context, h *DefinitionHolder, build *B
 		// Release notes.
 		relnoteCLsChecked := wf.Action0(wd, "Check for open release note fragment CLs", cycle.CheckRelnoteCLs)
 		nextRelnote := wf.Task2(wd, "Merge release note fragments and add to x/website", cycle.MergeNextRelnoteAndAddToWebsite, devVer, coordinators, wf.After(relnoteCLsChecked))
-		wf.Action3(wd, "Remove release note fragments from main repo", cycle.RemoveNextRelnoteFromMainRepo, devVer, nextRelnote, coordinators)
+		relnoteTest := wf.After(nextAPI) // cmd/relnote.TestCheckAPIFragments needs the API promotion to happen first.
+		wf.Action3(wd, "Remove release note fragments from main repo", cycle.RemoveNextRelnoteFromMainRepo, devVer, nextRelnote, coordinators, relnoteTest)
 
 		h.RegisterDefinition(fmt.Sprintf("between freeze start and RC 1 for Go 1.%d", currentMajor+1), wd)
 	}