Logging to progress bar doesn't work when calling trainer.test()
🐛 Bug
The metric logged by EvalResult.log() doesn't show up in the progress bar when setting prog_bar=True.
Code sample
import time
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.utils.data import TensorDataset, DataLoader
import pytorch_lightning as pl

class MyModel(pl.LightningModule):
    def __init__(self):
        super(MyModel, self).__init__()
        self.layer = nn.Linear(64, 1)

    def forward(self, x):
        return self.layer(x)

    def test_step(self, batch, batch_idx):
        X, y = batch
        loss = F.mse_loss(self.forward(X), y)

        result = pl.EvalResult()
        result.log("test_loss", loss, prog_bar=True)
        time.sleep(1)
        return result

test_ds = TensorDataset(torch.randn(64 * 5, 64), torch.randn(64 * 5, 1))
test_loader = DataLoader(test_ds, batch_size=64)

model = MyModel()
trainer = pl.Trainer(logger=False)
trainer.test(model, test_dataloaders=test_loader)

Expected behavior
test_loss shows up in the progress bar when running the above script.
Environment

PyTorch Version: 1.6
OS: Linux
How you installed PyTorch: pip
Python version: 3.8.5