run-task overrides fails to evaluate env arguments

[dsvensson]

Orb version:

2.2.1

What happened:

Error parsing parameter '--overrides': Expected: '=', received: '$' for input:
$OVERRIDES
^

Expected behavior:

I expected that this would work:

      - run:
          name: "foo"
          command: echo "export OVERRIDES=\"test\"" >> $BASH_ENV
      - aws-ecs/run-task:
          overrides: "${OVERRIDES}"
          ...