Fix handling of next-version-from-metadata option

The `--next-version-from-metadata` option correctly reads the repo's metadata
to define `config.nextVersion` when `loadConfig` is called. However, it is
immediately overridden on the next line by `argv["next-version"]` which
defaults to "Unreleased" and thus is always truthy.

src/cli.ts

@@ -66,7 +66,7 @@ export async function run() {
       nextVersionFromMetadata: argv["next-version-from-metadata"],
     });
 
-    if (argv["next-version"]) {
+    if (argv["next-version"] !== NEXT_VERSION_DEFAULT) {
       config.nextVersion = argv["next-version"];
     }