Fix: Preserve user input in dynamic inputs without options

What does this MR do and why?

Fixes an issue where user input was being reset for dynamic inputs that use spec:inputs:rules without defining options. Previously, when a rule matched but had no options array, the validation logic incorrectly treated any user-entered value as invalid and reset it.

#584868 (closed)

How to set up and validate locally

1. Create a CI config with dynamic inputs using rules without options:

   spec:
     inputs:
       deployment_type:
         options: ['standard', 'custom']
         default: 'standard'
       custom_config:
         rules:
           - if: $[[ inputs.deployment_type ]] == 'custom'
             default: null

2. Run a new pipeline and select custom for deployment_type

3. Enter text in custom_config - it should now be preserved

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