chore: escape username using backticks in changelog (#2336)

The motivation behind this is that GitHub mentions in PR descriptions trigger notifications for every contributor for every release because their username is part of the changelog.

cliff.toml

@@ -34,7 +34,7 @@ body = """
 {% macro commit(commit) -%}
 - [{{ commit.id | truncate(length=7, end="") }}]({{ "https://github.com/ratatui/ratatui/commit/" ~ commit.id }}) \
   *({{commit.scope | default(value = "uncategorized") | lower }})* {{ commit.message | upper_first | trim }}\
-  {% if commit.remote.username %} by @{{ commit.remote.username }}{%- endif -%}\
+  {% if commit.remote.username %} by `@{{ commit.remote.username }}`{%- endif -%}\
   {% if commit.remote.pr_number %} in [#{{ commit.remote.pr_number }}]({{ self::remote_url() }}/pull/{{ commit.remote.pr_number }}){%- endif %}\
 {%- if commit.breaking %} [**breaking**]{% endif %}
 {%- if commit.body %}\n\n{{ commit.body | indent(prefix="  > ", first=true, blank=true) }}