hardware-observer charm pinned to rev70 to unblock CI

[ca-scribner]

Bug Description

As discussed in #161, integration tests are failing with the most recent hardware-observer revision. CI will now be pinned to the working rev70 until this can be resolved.

this issue is filed in hardware-observer to identify if this behaviour is a bug

To Reproduce

tox -e integration

Environment

Relevant log output

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Additional context