This test was incorrectly assuming that the interface `socket_idname`
matches the socket `idname`, but it generally should not include the
subtype any more.
Loading pre-4.0.20 node groups with sockets using subtypes causes
broken socket identifiers. This is because the node tree interface now
expects sockets to use the base identifiers ("NodeSocketFloat" instead
of "NodeSocketFloatFactor" etc.).
To correct this the conversion code now replaces socket idnames that
include a subtype suffix with their base names. This fix is also applied
to files between versions 4.0.20 and 4.1.10, where the socket types
may have been converted incorrectly.
Lukas Tönne