fix: packages: py-flatbuffers: require: @25.9.23 for py-setuptools

Author: wdconinc

spack-environment/packages.yaml

@@ -356,6 +356,9 @@ packages:
   py-epic-capybara:
     require:
     - '@git.ef2a8790312b9b697655b28a07b353e601bfa3b8'
+  py-flatbuffers:
+    require:
+    - '@25.9.23:'
   py-hepunits:
     require:
     - '@2.3.2:'