[CI] make runner_type restricted. (#9441)

make runner_type restricted.

Author: sayakpaul

.github/workflows/ssh-runner.yml

@@ -4,8 +4,12 @@ on:
   workflow_dispatch:
     inputs:
       runner_type:
-        description: 'Type of runner to test (a10 or t4)'
+        description: 'Type of runner to test (aws-g6-4xlarge-plus: a10 or aws-g4dn-2xlarge: t4)'
+        type: choice
         required: true
+        options:
+          - aws-g6-4xlarge-plus
+          - aws-g4dn-2xlarge
       docker_image:
         description: 'Name of the Docker image'
         required: true