Add github gpu ci tests

Summary:
Pull Request resolved: #5292

Add github gpu tests from circleci

Reviewed By: wat3rBro

Differential Revision: D57582764

fbshipit-source-id: 02c2bb5e5a6435a95b7683603040f33a8dc02526

Author: Eric Zhang

.github/actions/uninstall_tests/action.yml

@@ -9,4 +9,4 @@ runs:
       # Remove built binaries
       rm -rf build/ detectron2/*.so
       # Tests that code is importable without installation
-      PYTHONPATH=. ./.circleci/import-tests.sh
+      . ./.github/import-tests.sh

.github/import-tests.sh

@@ -0,0 +1,16 @@
+#!/bin/bash -e
+# Copyright (c) Facebook, Inc. and its affiliates.
+
+# Test that import works without building detectron2.
+
+# Check that _C is not importable
+python -c "from detectron2 import _C" > /dev/null 2>&1 && {
+  echo "This test should be run without building detectron2."
+  exit 1
+}
+
+# Check that other modules are still importable, even when _C is not importable
+python -c "from detectron2 import modeling"
+python -c "from detectron2 import modeling, data"
+python -c "from detectron2 import evaluation, export, checkpoint"
+python -c "from detectron2 import utils, engine"