[AI Agent Task] AIAgent Skills Inline don't work

### Describe the issue

Steps to reproduce:
1. Run the example
2. Throws INVALID ARGUMENT 400 error

```yaml
id: agent_with_skills
namespace: company.ai

tasks:
- id: agent
type: io.kestra.plugin.ai.agent.AIAgent
prompt: "Translate the following text to French - 'Hello, how are you today?'"
provider:
type: io.kestra.plugin.ai.provider.GoogleGemini
modelName: gemini-3.5-flash-lite
apiKey: "{{ secret('GEMINI_API_KEY') }}"
tools:
- type: io.kestra.plugin.ai.tool.Skill
skills:
- name: translation_expert
description: Expert translator for multiple languages
content: |
You are an expert translator. When translating text:
1. Preserve the original meaning and tone
2. Use natural phrasing in the target language
3. Keep proper nouns unchanged
```

It works for reading skills from a file though so bug with `content`?

Related: https://github.com/kestra-io/docs/issues/5368

### Environment

- Kestra Version: 2.0 RC10 EE

Start by running the provided agent_with_skills example with the inline Skill content and compare it with the file-based skills case, which reportedly works. Trace how the Skill tool handles the content field and verify completion by confirming the inline example no longer returns INVALID ARGUMENT 400 while preserving file-based behavior.

Written by the indexing model from the issue text.