red flag says `not signed` even when it is signed, but unknown signature key.

[rampall]

Red flag in the install page says a package is not signed even when it is actually signed (but the signature key is not known).
It would be less confusing for users if the text was more specific.

Describe the bug

To Reproduce

Expected behavior

Screenshots

DAppNode version:

• Package version:
• OS:
• Browser

Additional context