Relax upper bound for text-iso8601 to 0.3

[dancewithheart]

Verified with:

cabal build all
cabal test all

With this change cabal-audit no longer reports HSEC-2026-0007:

Hackage package text-iso8601 at version 0.1.1.1 is vulnerable for:
  HSEC-2026-0007 "Denial of Service and Memory Exhaustion in aeson and text-iso8601"
  published: 2026-05-22 07:02:58 UTC
  https://haskell.github.io/security-advisories/advisory/HSEC-2026-0007
  Fix available since version 0.2.0.0
  aeson, text-iso8601, dos, memory-exhaustion, json