Revert "chore: edm4eic 6.0.0"

This reverts commit 513cc448.

This commit went into master instead of a PR by mistake. The current EICrecon was not forward-compatible with EDM4eic 6.0.0. Reverting to get back to a valid state.

spack-environment/packages.yaml

@@ -84,7 +84,7 @@ packages:
     - '@656aa3192b097a631ddd1e0380e80c26fd6644a7'
   edm4eic:
     require:
-    - '@6.0.0' # EDM4EIC_VERSION
+    - '@5.0.0' # EDM4EIC_VERSION
     - cxxstd=20
   edm4hep:
     require: