The (internal) Grisu module was removed in Julia 1.6. However, some packages relies on this module. To keep this working, the Grisu module was filtered out as a normal package that can be depended on.
Use it as follows, add a dependency on Grisu and use this instead of normally loading it:
if isdefined(Base, :Grisu)
import Base.Grisu
else
import Grisu
end