With implicit conversion of tagged integers to untagged ones going away,
explicitly tag (or untag, as necessary) the operands of the following
operations, in "test/raft/randomized_nemesis_test.cc":
- addition of tagged and untagged (both should be tagged)
- taking the minimum of an index difference and a container size (both
should be untagged)
Signed-off-by: Laszlo Ersek <laszlo.ersek@scylladb.com>