scale: fixed a bug where evals could be created with wrong type. (#17092)

The job scale RPC endpoint hard-coded the eval creation to use the
type of service. This meant scaling events triggered on jobs of
type batch would create evaluations with the wrong type, which
does not seem to cause any problems, just confusion when
correlating the two.

.changelog/17092.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+scale: Fixed a bug where evals could be created with the wrong type
+```

nomad/job_endpoint.go

@@ -1152,7 +1152,7 @@ func (j *Job) Scale(args *structs.JobScaleRequest, reply *structs.JobRegisterRes
 				ID:             uuid.Generate(),
 				Namespace:      namespace,
 				Priority:       job.Priority, // Safe as nil check performed above.
-				Type:           structs.JobTypeService,
+				Type:           job.Type,
 				TriggeredBy:    structs.EvalTriggerScaling,
 				JobID:          args.JobID,
 				JobModifyIndex: reply.JobModifyIndex,

nomad/job_endpoint_test.go

@@ -7868,6 +7868,44 @@ func TestJobEndpoint_Scale_SystemJob(t *testing.T) {
 		`400,cannot scale jobs of type "system"`)
 }
 
+func TestJobEndpoint_Scale_BatchJob(t *testing.T) {
+	ci.Parallel(t)
+
+	testServer, testServerCleanup := TestServer(t, nil)
+	defer testServerCleanup()
+	codec := rpcClient(t, testServer)
+	testutil.WaitForLeader(t, testServer.RPC)
+	state := testServer.fsm.State()
+
+	mockBatchJob := mock.BatchJob()
+	must.NoError(t, state.UpsertJob(structs.MsgTypeTestSetup, 10, nil, mockBatchJob))
+
+	scaleReq := &structs.JobScaleRequest{
+		JobID: mockBatchJob.ID,
+		Target: map[string]string{
+			structs.ScalingTargetGroup: mockBatchJob.TaskGroups[0].Name,
+		},
+		Count: pointer.Of(int64(13)),
+		WriteRequest: structs.WriteRequest{
+			Region:    DefaultRegion,
+			Namespace: mockBatchJob.Namespace,
+		},
+	}
+	var resp structs.JobRegisterResponse
+	must.NoError(t, msgpackrpc.CallWithCodec(codec, "Job.Scale", scaleReq, &resp))
+
+	// Pull the generated evaluation from state and ensure the detailed type
+	// matches the jobspec.
+	testFMSSnapshot, err := testServer.fsm.State().Snapshot()
+	must.NoError(t, err)
+
+	scaleEval, err := testFMSSnapshot.EvalByID(nil, resp.EvalID)
+	must.NoError(t, err)
+	must.Eq(t, resp.EvalID, scaleEval.ID)
+	must.Eq(t, mockBatchJob.ID, scaleEval.JobID)
+	must.Eq(t, mockBatchJob.Type, scaleEval.Type)
+}
+
 func TestJobEndpoint_InvalidCount(t *testing.T) {
 	ci.Parallel(t)
 	require := require.New(t)