ci: Fix license check false pass

The license check workflow quietly stopped working after commit
8f66f854. Upgrading the checkout action
changed default behavior to only fetch one commit instead of all history
for all branches, which caused an uncaught fatal error in the scancode
action:

fatal: ambiguous argument 'origin/main..': unknown revision or path not
in the working tree.

The scancode action then completed successfully having not actually
checked anything.

Fix this by setting the checkout action fetch depth to 0, similar to
other workflows.

Signed-off-by: Maureen Helm <maureen.helm@analog.com>