Please revise base bound to support GHC 9.10

[tomjaguarpaw]

This works fine, so I guess the upper bound on base should be bumped to base < 4.21:

cabal repl -z -b indexed-traversable==0.1.3 --allow-newer=indexed-traversable:base -w ~/ghc-9.10/bin/ghc-9.10.1

[phadej]

Resolved by #42