jobs: new naming scheme for ftp.osmocom.org keys

Use new ssh keys for ftp.osmocom.org with consistent naming scheme. It
was not possible to use @ in the ID name for new IDs, so I've used an
underscore instead.

Change-Id: Id0cf70e70944cf1a1963e0046b1470a0485c05f8

jobs/osmocom-api.yml

@@ -15,7 +15,7 @@
     wrappers:
     - ssh-agent-credentials:
         users:
-        - api@osmocom
+        - api_ftp.osmocom.org
     parameters:
       - string:
           name: BRANCH

jobs/osmocom-release-tarballs.yml

@@ -42,6 +42,6 @@
     wrappers:
       - ssh-agent-credentials:
           users:
-          - releases
+          - releases_ftp.osmocom.org
 
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