`brew bump` understands that some formulae/casks are skipped by
livecheck but it doesn't use this information to avoid doing
unnecessary or inappropriate work. This modifies related logic to not
fetch PR information or try to open a version bump PR if livecheck is
skipped. livecheck is our only source of version information these
days, so we can't try to version bump a package if we don't have
upstream version information.
This has been leading to an "Invalid usage: `--version` must not be
empty" error and this _should_ fix the issue under these particular
circumstances. There's still plenty of room for improvement in how
all of this is handled in bump but this is just a quick bug fix.
1d47038b12