fix: Google Vertex - fix the content type of ChatMessage content from function

[anakin87]

Related Issues

• part of Update all components with ChatMessage to use text instead of content #1236 (accessing text instead of content)
• twin PR of fix: GoogleAI - fix the content type of ChatMessage content from function #1241 (see it for details and review it first)
  • I noticed that in messages from function, the content is a dict instead of str (see Haystack ChatMessage definition). This happened also because in integrations we skipping mypy checks for Haystack (this is not easy to fix)

Proposed Changes:

• fix the content type
• use text instead of content to access the text

How did you test it?

CI

Notes for the reviewer

• This is a bug fix but also a breaking change. To make things clearer, I think that we can release a major version
• In the future, when new ChatMessage + Tool are adopted, we should refactor the tool calling section of this Chat Generator and I'm confident that we can handle it better

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[vblagoje]

Looks good! One change is that we previously, for some reason, dumped dict to content directly (which was a mistake) but now are properly json string serializing it. Isn't this going to break some existing clients? Even if it does - it's for the better, right?

[anakin87]

Yes, this can potentially break the existing behavior. But it is actually a bug fix.
That is why I will release a new major version.