fix: pin substrate-interface to < 1.8.0

[odesenfans]

There appears to be a bug in the 1.8.0 version that was just pushed minutes ago by the Substrate team. This breaks our CI. Pinning to below 1.8 for now.

[1yam]

LGTM

[github-actions]

"summary": "This PR includes a minor change to the substrate-interface dependency version, which is unlikely to introduce bugs. The updated version constraint substrate-interface<1.8 suggests a focus on maintaining compatibility within the constraints of the current project requirements, which aligns with the 'BLUE' category of review complexity.",
"highlights": [
{
"line": "index 24012413..46adc715",
"comment": "File and line number change indicating a straightforward update."
},
{
"line": "substrate-interface<1.8",
"comment": "Version constraint update suggesting a minor adjustment to dependencies."
}
]
}