bug 1432265 - fix fx source signing. r=bhearsum

MozReview-Commit-ID: 5f9ILHKkpVG

--HG--
extra : source : c94e1fd9fe7a47c51c421db2a7052292ac411e3a
extra : histedit_source : 7a1b7f2108be5ccf22ef6cd27c0117fb024fea4b

taskcluster/taskgraph/util/scriptworker.py

@@ -488,7 +488,7 @@ def get_release_config(config):
 def get_signing_cert_scope_per_platform(build_platform, is_nightly, config):
     if 'devedition' in build_platform:
         return get_devedition_signing_cert_scope(config)
-    elif is_nightly:
+    elif is_nightly or build_platform in ('linux64-source', 'linux64-fennec-source'):
         return get_signing_cert_scope(config)
     else:
         return add_scope_prefix(config, 'signing:cert:dep-signing')