test(changelog): add --no-incremental regression test, address review feedback

- Add test_changelog_no_incremental_overrides_config_with_revision covering
  --no-incremental combined with a rev_range when changelog_incremental=true
  is set in config.
- Clarify the comment in Changelog.__init__ to explicitly reference the
  --no-incremental flag needed to opt out.
- Regenerate the stale docs/images/cli_help/cz_changelog___help.svg
  screenshot to include the new --no-incremental option.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bearomorphism

commitizen/commands/changelog.py

@@ -81,8 +81,8 @@ def __init__(self, config: BaseConfig, arguments: ChangelogArgs) -> None:
         # `--incremental`/`--no-incremental` on the CLI always takes precedence over
         # the `changelog_incremental` setting. When neither flag is passed, the
         # argument is `None` and we fall back to the config value. This lets a
-        # one-off invocation (e.g. `cz changelog <rev_range>`) opt out of an
-        # incremental default enabled in the configuration.
+        # one-off invocation (e.g. `cz changelog --no-incremental <rev_range>`) opt
+        # out of an incremental default enabled in the configuration.
         incremental_arg = arguments.get("incremental")
         self.incremental = (
             incremental_arg