Revert "Revert "Cache $CARGO_HOME""

This reverts commit 248c23039c.

.taskcluster.yml

@@ -18,6 +18,8 @@ tasks:
         source: ${event.compare}
       scopes:
         - "queue:create-task:aws-provisioner-v1/github-worker"
+        - "docker-worker:cache:cargo-registry-cache"
+        - "docker-worker:cache:cargo-git-cache"
 
       payload:
         maxRunTime: 600

decision-task/run.py

@@ -36,7 +36,16 @@ def create_task(name, command, artifacts=None, dependencies=None, env=None):
             "owner": event["pusher"]["name"] + "@users.noreply.github.com",
             "source": event["compare"],
         },
+        # https://docs.taskcluster.net/docs/reference/workers/docker-worker/docs/caches
+        "scopes": [
+            "docker-worker:cache:cargo-registry-cache",
+            "docker-worker:cache:cargo-git-cache",
+        ],
         "payload": {
+            "cache": {
+                "cargo-registry-cache": "/root/.cargo/registry",
+                "cargo-git-cache": "/root/.cargo/git",
+            },
             "maxRunTime": 600,
             "image": "buildpack-deps:bionic",
             "command": [