Make sure platform is correct for packaging env

When archiving the environments, we get the platform from the conda
environment, so we need it to be the correct platform. This only
currently applies when building for osx-64 an a osx-arm64 machine.

Author: jclarkeSTFC

buildconfig/Jenkins/Conda/mamba-utils

@@ -20,7 +20,7 @@ setup_mamba () {
   source $install_prefix/etc/profile.d/mamba.sh
 
   if [ -n "$env_name" ]; then
-    create_and_activate_env "$env_name"
+    create_and_activate_env "$env_name" "$platform"
   fi
 }
 
@@ -34,6 +34,10 @@ create_and_activate_env() {
   local conda_subdir_str=$2
   CONDA_SUBDIR=$conda_subdir_str mamba create --yes --name $env_name
   mamba activate $env_name
+
+  if [[ -n "$conda_subdir_str" ]]; then
+    conda config --env --set subdir "$conda_subdir_str"
+  fi
 }
 
 # Build the mantid-developer metapackage from source and
@@ -53,10 +57,5 @@ create_and_activate_mantid_developer_env() {
 
   $SCRIPT_DIR/package-conda "$packaging_dir" --build-mantid-developer --platform "$platform"
   create_and_activate_env mantid-developer "$platform"
-
-  if [[ -n "$platform" ]]; then
-    conda config --env --set subdir "$platform"
-  fi
-
   mamba install -c "$packaging_dir"/conda-bld mantid-developer --yes
 }