_auto_deps: bump foolscap to >=0.6.3 to tolerate twisted-12.0.0

_auto_deps: bump foolscap to >=0.6.3 to tolerate twisted-12.0.0

The current Twisted release is 12.1.0, which (like 12.0.0 before it)
isn't compatible with foolscap-0.6.2 and earlier. We previously required
foolscap>=0.6.1, since that's all we actually need from foolscap itself.
_auto_deps specifies twisted>=11.0.0, so any system that can't meet that
will install the current Twisted (12.1.0), which will give them
something incompatible with foolscap-0.6.1 and 0.6.2 .

If we're limited to setuptools's declarative constraint language (and
can't have a function which evaluates the available dependency versions
and gives recommendations on which to change), then the only safe
approach is to make sure that any acceptable Foolscap version will be
compatible with all acceptable Twisted versions. So, bump the foolscap
dependency to >=0.6.3, which covers all currently-known
incompatibilities.