fix(release): 🐛 list contributors even when GitHub can't resolve a login

The previous fix stopped the changelog crash but left the section
empty whenever github.contributors' username is null for everyone
(e.g. v1.2.0 -- commit author email isn't linked to a verified GitHub
account, so the API never resolves a login). Source the list from
commits' own author.name instead (always present), deduped, still
preferring @username when a commit's github.username did resolve.

Author: lguerard

cliff.toml

@@ -8,11 +8,13 @@ body = """
 - {% if commit.scope %}**{{ commit.scope }}**: {% endif %}{{ commit.message | split(pat="\n") | first }}
 {% endfor %}
 {% endfor %}\
-{% if github.contributors | length > 0 %}
+{% set contributor_commits = commits | unique(attribute="author.name") %}
+{% if contributor_commits | length > 0 %}
 ### 👥 Contributors
 
-{% for contributor in github.contributors %}\
-{% if contributor.username %}* @{{ contributor.username }}
+{% for c in contributor_commits %}\
+{% if c.github.username %}* @{{ c.github.username }}
+{% else %}* {{ c.author.name }}
 {% endif %}\
 {% endfor %}
 {% endif %}\