No bug: [try-staging] Allow staging builds to access staging github ssh key; r=nthomas

The secret with the ssh key already exists in taskcluster, this tells
mozharness to try to access it.

Differential Revision: https://phabricator.services.mozilla.com/D25700

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

testing/mozharness/configs/partner_repacks/release_mozilla-release_desktop.py

@@ -7,7 +7,7 @@ config = {
         {
             "filename": "/builds/partner-github-ssh",
             "secret_name": "project/releng/gecko/build/level-%(scm-level)s/partner-github-ssh",
-            "min_scm_level": 3,
+            "min_scm_level": 1,
             "mode": 0o600,
         },
     ],

testing/mozharness/configs/partner_repacks/release_mozilla-release_desktop_EME-free.py

@@ -7,7 +7,7 @@ config = {
         {
             "filename": "/builds/partner-github-ssh",
             "secret_name": "project/releng/gecko/build/level-%(scm-level)s/partner-github-ssh",
-            "min_scm_level": 3,
+            "min_scm_level": 1,
             "mode": 0o600,
         },
     ],

testing/mozharness/configs/partner_repacks/staging_release_mozilla-release_desktop.py

@@ -7,7 +7,7 @@ config = {
         {
             "filename": "/builds/partner-github-ssh",
             "secret_name": "project/releng/gecko/build/level-%(scm-level)s/partner-github-ssh",
-            "min_scm_level": 3,
+            "min_scm_level": 1,
             "mode": 0o600,
         },
     ],