Update for zephyr 3.7

[szczys]

Change board names to use forward slash instead of underscore to match new device model for Zephyr v3.7.0.

This should not be merged until Golioth Firmware SDK v0.15.0 is released.

resolves https://github.com/golioth/firmware-issue-tracker/issues/618

[github-actions[bot]]

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