fix: undefined variable for single env workflows

Author: jackhodgkiss

roles/github/templates/generic.yml.j2

@@ -8,6 +8,9 @@
 <%- set _ = github_default_kayobe_arguments.update({"KAYOBE_VAULT_PASSWORD": "${{ secrets[format('{0}_KAYOBE_VAULT_PASSWORD', inputs.kayobe_environment)] }}" }) -%>
 <%- set _ = github_kayobe_arguments.update({"KAYOBE_ENVIRONMENT": '${{ inputs.kayobe_environment }}'}) -%>
 <%- endif -%>
+<%- if github_environment_selector == 'single' -%>
+<%- set _ = github_kayobe_arguments.update({"KAYOBE_ENVIRONMENT": github_kayobe_environments | first}) -%>
+<%- endif -%>
 name: %% format_file_name(workflow.file_name, is_title=true) %%
 
 on: