Bug 1533818 - Don't try to expand from a 'cose.manifest' file when repacking the l10n copy of omni.ja. r=aki

Differential Revision: https://phabricator.services.mozilla.com/D34697

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozpack/chrome/manifest.py

@@ -364,4 +364,5 @@ def is_manifest(path):
     Return whether the given path is that of a manifest file.
     '''
     return path.endswith('.manifest') and not path.endswith('.CRT.manifest') \
-        and not path.endswith('.exe.manifest')
+        and not path.endswith('.exe.manifest') \
+        and os.path.basename(path) != "cose.manifest"