pmb.parse.arguments: fix pkgname autocompletion (!1905)

Use pmb.helpers.args.add_cache() with the args used during
autocompletion, so pmb.helpers.pmaports._find_apkbuilds() does not fail
when trying to access args.cache.

pmb/parse/arguments.py

@@ -309,6 +309,7 @@ def package_completer(prefix, action, parser, parsed_args):
     args = parsed_args
     pmb.config.merge_with_args(args)
     pmb.helpers.args.replace_placeholders(args)
+    pmb.helpers.args.add_cache(args)
     packages = set(
         package for package in pmb.helpers.pmaports.get_list(args)
         if package.startswith(prefix))