In Ansible, how to add a block of text at end of a file with a blank line before the marker?

I have a playbook as shown below:

- hosts: localhost
  tasks:
    - name: update a file
      blockinfile:
        dest: /tmp/test
        block: |
          line 1
          line 2

Upon running the playbook, the file /tmp/test becomes:

a # this is the end line of the original file
# BEGIN ANSIBLE MANAGED BLOCK
line 1
line 2
# END ANSIBLE MANAGED BLOCK

I would like to add a blank line (newline) before the marker "# BEGIN ANSIBLE MANAGED BLOCK" for visual effect.
What is the easiest way to do it? Preferably within the task, but any idea is welcome. If I redefine the marker, it will affect both the "BEGIN" and "END" marker.

If you have a file that looks like this:

some line
foobar
some other line

and you want to add a newline before the pattern "foobar" in this example, the following ansible code will do it for you:

- hosts: localhost
  gather_facts: no
  connection: local
  tasks:
    - name: update a file
      replace:
        dest: /tmp/foobar
        regexp: |
          (?mx)     # "m" lets ^ and $ match next to imbedded \n, x allows white space for readability
          (?<!\n\n) # a Zero-Length Assertion that it does not have an empty line already
          ^         # beginning of the line
          (foobar)  # match "foobar" and save it as \1, it could be "\#\ BEGIN\ ANSIBLE\ MANAGED\ BLOCK" if that is your pattern
          $         # end of line
        replace: "\n\\1" # add a newline before the matched pattern

and it is idempotent and it does not add the newline at the end of the file when the pattern is not present.