Remove no-longer-relevant base_sha input parameter

Now that we are not testing file changes, the parameter is not needed.

Author: mhucka

.github/workflows/ci.yaml

@@ -34,10 +34,6 @@ on:
 
   workflow_dispatch:
     inputs:
-      base_sha:
-        description: 'SHA of base commit to run against:'
-        type: string
-        required: true
       debug:
         description: 'Run with debugging options'
         type: boolean