[CircleCI] Update base images to ubuntu-2004 (#5802)

As Ubuntu-1604 runners will no longer be available in early May 2022
Update `ubuntu-1604:201903-01` to `ubuntu-2004:202104-01`
and `ubuntu-1604-cuda-10.2:202012-01` to `ubuntu-2004-cuda-11.4:202110-01`
Per [CircleCI Configuration reference](https://circleci.com/docs/2.0/configuration-reference/)

.circleci/config.yml

@@ -673,7 +673,7 @@ jobs:
 
   smoke_test_docker_image_build:
     machine:
-      image: ubuntu-1604:201903-01
+      image: ubuntu-2004:202104-01
     resource_class: large
     environment:
       image_name: torchvision/smoke_test
@@ -784,7 +784,7 @@ jobs:
   unittest_linux_gpu:
     <<: *binary_common
     machine:
-      image: ubuntu-1604-cuda-10.2:202012-01
+      image: ubuntu-2004-cuda-11.4:202110-01
     resource_class: gpu.nvidia.medium
     environment:
       image_name: "pytorch/manylinux-cuda102"
@@ -975,7 +975,7 @@ jobs:
   cmake_linux_gpu:
     <<: *binary_common
     machine:
-      image: ubuntu-1604-cuda-10.2:202012-01
+      image: ubuntu-2004-cuda-11.4:202110-01
     resource_class: gpu.nvidia.small
     environment:
       PYTHON_VERSION: << parameters.python_version >>

.circleci/config.yml.in

@@ -673,7 +673,7 @@ jobs:
 
   smoke_test_docker_image_build:
     machine:
-      image: ubuntu-1604:201903-01
+      image: ubuntu-2004:202104-01
     resource_class: large
     environment:
       image_name: torchvision/smoke_test
@@ -784,7 +784,7 @@ jobs:
   unittest_linux_gpu:
     <<: *binary_common
     machine:
-      image: ubuntu-1604-cuda-10.2:202012-01
+      image: ubuntu-2004-cuda-11.4:202110-01
     resource_class: gpu.nvidia.medium
     environment:
       image_name: "pytorch/manylinux-cuda102"
@@ -975,7 +975,7 @@ jobs:
   cmake_linux_gpu:
     <<: *binary_common
     machine:
-      image: ubuntu-1604-cuda-10.2:202012-01
+      image: ubuntu-2004-cuda-11.4:202110-01
     resource_class: gpu.nvidia.small
     environment:
       PYTHON_VERSION: << parameters.python_version >>