---
- name: Gather OS specific variables
  include_vars: "{{ item }}"
  with_first_found:
    - "{{ ansible_distribution|lower }}-{{ ansible_distribution_version }}.yml"
    - "{{ ansible_distribution|lower }}-{{ ansible_distribution_major_version }}.yml"
    - "{{ ansible_distribution|lower }}.yml"
    - "{{ ansible_os_family|lower }}.yml"

- name: Define netbox_packages
  set_fact:
    netbox_packages: "{{ _netbox_packages | list }}"
  when: netbox_packages is not defined

- name: Define netbox_python_packages
  set_fact:
    netbox_python_packages: "{{ _netbox_python_packages | list }}"
  when: netbox_python_packages is not defined

- name: Define netbox_python_binary
  set_fact:
    netbox_python_binary: "{{ _netbox_python_binary }}"
  when: netbox_python_binary is not defined

- name: Define netbox_ldap_packages
  set_fact:
    netbox_ldap_packages: "{{ _netbox_ldap_packages | list }}"
  when: netbox_ldap_packages is not defined

- name: Identify current execution PATH
  shell: "echo $PATH"
  register: _path_exec
  changed_when: false

- name: Set a fact for current execution PATH
  set_fact:
    _path: "{{ _path_exec.stdout }}"

---
- name: Gather OS specific variables
  include_vars: "{{ item }}"
  with_first_found:
    - "{{ ansible_distribution|lower }}-{{ ansible_distribution_version }}.yml"
    - "{{ ansible_distribution|lower }}-{{ ansible_distribution_major_version }}.yml"
    - "{{ ansible_distribution|lower }}.yml"
    - "{{ ansible_os_family|lower }}.yml"

- name: Define netbox_packages
  set_fact:
    netbox_packages: "{{ _netbox_packages | list }}"
  when: netbox_packages is not defined

- name: Define netbox_python_packages
  set_fact:
    netbox_python_packages: "{{ _netbox_python_packages | list }}"
  when: netbox_python_packages is not defined

- name: Define netbox_python_binary
  set_fact:
    netbox_python_binary: "{{ _netbox_python_binary }}"
  when: netbox_python_binary is not defined

- name: Define netbox_ldap_packages
  set_fact:
    netbox_ldap_packages: "{{ _netbox_ldap_packages | list }}"
  when: netbox_ldap_packages is not defined

- name: Identify current execution PATH
  shell: "echo $PATH"
  register: _path_exec
  changed_when: false
  check_mode: false

- name: Set a fact for current execution PATH
  set_fact:
    _path: "{{ _path_exec.stdout }}"
  check_mode: false

Allow role to run successfully in --check mode
Allow role to run successfully in --check mode

In check-mode, the register task for _path_exec isn't executed, which then fails the set_fact task after it.
Since these are safe to run in check-mode, i've added the check_mode:false flag.