fix(changelog): add CI-only trailing newline for prepend

Render an extra trailing newline from the git-cliff body template when
running in GitHub Actions so --prepend separates new release notes from
existing changelog content.

Author: jobcespedes

release/changelog/cliff.toml

@@ -9,6 +9,7 @@ body = """
 {%- set version_prefix = get_env(name="CLIFF_VERSION_PREFIX", default="v") -%}
 {%- set gh_url = get_env(name="GITHUB_SERVER_URL", default="https://github.com") ~ "/" ~ get_env(name="GITHUB_REPOSITORY", default="") -%}
 {%- set use_emojis = get_env(name="CLIFF_USE_EMOJIS", default="false") == "true" -%}
+{%- set github_actions = get_env(name="GITHUB_ACTIONS", default="false") == "true" -%}
 {% if version %}\
     {%- set ver_stripped = version | trim_start_matches(pat=version_prefix) -%}
     {%- set ver = version_prefix ~ ver_stripped -%}
@@ -30,6 +31,8 @@ body = """
             ([`{{ commit.id | truncate(length=7, end="") }}`]({{ gh_url }}/commit/{{ commit.id }}))\
     {% endfor %}
 {% endfor %}
+{%- if github_actions %}
+{% endif %}
 """
 # Remove leading and trailing whitespaces from the changelog's body.
 trim = true