ansible cannot store the externally obtained string "yes" as-is as "fact"

ansible-convert-externally-obtained-string-yes-to-true.yml

---
- name: host
  hosts: localhost
  gather_facts: false

  tasks:
    - block:
        - name: show ansible version
          ansible.builtin.debug:
            var: ansible_version.full

        - name: create "yes.txt" which content is "yes"
          ansible.builtin.copy:
            dest: "yes.txt"
            content: "yes"
            mode: 0644

        - name: load content of "yes.txt"
          ansible.builtin.slurp:
            path: "yes.txt"
          register: slurped_yes

        - name: show content of "yes.txt"
          ansible.builtin.debug:
            msg: "{{ slurped_yes.content | b64decode }}"

        - name: set content of yes.txt as "should_be_string_yes" fact
          ansible.builtin.set_fact:
            should_be_string_yes: "{{ slurped_yes.content | b64decode }}"

        - name: show value of "should_be_string_yes" fact
          ansible.builtin.debug:
            var: should_be_string_yes

        - name: assert "should_be_string_yes" == "yes"
          ansible.builtin.assert:
            that:
              - should_be_string_yes == "yes"
      always:
        - name: delete created "yes.txt"
          ansible.builtin.file:
            path: "yes.txt"
            state: absent

Execution results with ansible 2.12.3:

% ansible-playbook ansible-convert-externally-obtained-string-yes-to-true.yml

PLAY [host] *****************************************************************************

TASK [show ansible version] *************************************************************
ok: [localhost] => {
    "ansible_version.full": "2.12.3"
}

TASK [create "yes.txt" which content is "yes"] ******************************************
changed: [localhost]

TASK [load content of "yes.txt"] ********************************************************
ok: [localhost]

TASK [show content of "yes.txt"] ********************************************************
ok: [localhost] => {
    "msg": "yes"
}

TASK [set content of yes.txt as "should_be_string_yes" fact] ****************************
ok: [localhost]

TASK [show value of "should_be_string_yes" fact] ****************************************
ok: [localhost] => {
    "should_be_string_yes": true
}

TASK [assert "should_be_string_yes" == "yes"] *******************************************
fatal: [localhost]: FAILED! => {
    "assertion": "should_be_string_yes == \"yes\"",
    "changed": false,
    "evaluated_to": false,
    "msg": "Assertion failed"
}

TASK [delete created "yes.txt"] *********************************************************
changed: [localhost]

PLAY RECAP ******************************************************************************
localhost                  : ok=7    changed=2    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0