Clarify workflow_dispatch input description

We are currently using 'Release tag' to describe the required input
to our `workflow_dispatch` trigger. This is inaccurate - this field
actually requires a 'Release id', which I discovered when testing
GCM Core `apt-get` deployments yesterday. Updating so that the
description doesn't confuse folks running the workflow for a release
that is not 'latest'.

Author: Lessley Dennington

.github/workflows/release-apt-get.yml

@@ -6,7 +6,7 @@ on:
   workflow_dispatch:
     inputs:
       release:
-        description: 'Release Tag'
+        description: 'Release Id'
         required: true
         default: 'latest'