Disable Circle CI via dummy config

.circleci/config

@@ -0,0 +1,14 @@
+# This config file is a dummy CircleCI config that does nothing. We migrated away from CircleCI to Github Actions.
+# But our release/0.10 branch still uses CircleCI, so we can't disable the service entirely and need some way
+# to disable it only for newer versions. That's what this file is doing.
+
+version: 2.1
+
+jobs:
+  build:
+    docker:
+      - image: circleci/node:11.12.0
+    steps:
+      - run:
+          name: Dummy
+          command: 'echo Not running any Circle CI'