Pin setuptools<81 in environment.yml to fix CI failure

cylc-flow 8.2.7 imports pkg_resources (from setuptools), but
setuptools >= 81 removed pkg_resources from its distribution.
The conda env was resolving to setuptools 82.0.0 which no longer
ships pkg_resources, causing:
  ModuleNotFoundError: No module named 'pkg_resources'

Pinning setuptools<81 ensures the conda env gets a version that
still bundles pkg_resources.

Co-authored-by: ilaflott <6273252+ilaflott@users.noreply.github.com>

Author: Copilot

environment.yml

@@ -5,6 +5,7 @@ channels:
 dependencies:
   - python
   - pip
+  - setuptools<81
   - noaa-gfdl::fre-cli
   - conda-forge::pyyaml
   - conda-forge::nco