chore(deps): update module google.golang.org/genai to v1.28.0 (#1572)

This PR contains the following updates:

| Package | Change | Age | Confidence |
|---|---|---|---|
|
[google.golang.org/genai](https://redirect.github.com/googleapis/go-genai)
| `v1.25.0` -> `v1.28.0` |
[![age](https://developer.mend.io/api/mc/badges/age/go/google.golang.org%2fgenai/v1.28.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/go/google.golang.org%2fgenai/v1.25.0/v1.28.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>googleapis/go-genai (google.golang.org/genai)</summary>

###
[`v1.28.0`](https://redirect.github.com/googleapis/go-genai/releases/tag/v1.28.0)

[Compare
Source](https://redirect.github.com/googleapis/go-genai/compare/v1.27.0...v1.28.0)

##### Features

- Add `NO_IMAGE` enum value to `FinishReason`
([4f65f45](4f65f457b4))
- Add thinking\_config for live
([54152b2](54152b2e65))

###
[`v1.27.0`](https://redirect.github.com/googleapis/go-genai/releases/tag/v1.27.0)

[Compare
Source](https://redirect.github.com/googleapis/go-genai/compare/v1.26.0...v1.27.0)

##### Features

- Add `ImageConfig` to `GenerateContentConfig`
([55399fd](55399fdab3))
- rename ComputerUse tool (early access)
([d976966](d976966523))

##### Bug Fixes

- fix system\_instruction mapping issue in batches module
([c862a6d](c862a6de53))

###
[`v1.26.0`](https://redirect.github.com/googleapis/go-genai/releases/tag/v1.26.0)

[Compare
Source](https://redirect.github.com/googleapis/go-genai/compare/v1.25.0...v1.26.0)

##### Features

- Add FunctionResponsePart & ToolComputerUse.excludedPredefinedFunctions
([8b97cef](8b97cefe46))
- Support Imagen 4 Ingredients on Vertex
([a9ab364](a9ab364b51))

##### Bug Fixes

- Expose `JOB_STATE_RUNNING` and `JOB_STATE_EXPIRED` for Gemini Batches
states
([26e0182](26e0182613))
- fix systemInstruction mapping issue in batch generate content. fixes
[#&#8203;505](https://redirect.github.com/googleapis/go-genai/issues/505)
([3997ea2](3997ea21bb))
- initialization of `pre_tuned_model_checkpoint_id` from tuning config.
([b093bcf](b093bcf876))
- Prevent adding `,string` JSON tag for `int64`/`uint64` fields in
`Schema` class. fixes
[#&#8203;511](https://redirect.github.com/googleapis/go-genai/issues/511)
[#&#8203;481](https://redirect.github.com/googleapis/go-genai/issues/481)
([3423dd3](3423dd359d))

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined),
Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/googleapis/genai-toolbox).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0MS4xMzAuMSIsInVwZGF0ZWRJblZlciI6IjQxLjEzMS45IiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->

docs/en/getting-started/quickstart/go/genAI/go.mod

@@ -4,7 +4,7 @@ go 1.24.6
 
 require (
 	github.com/googleapis/mcp-toolbox-sdk-go v0.3.0
-	google.golang.org/genai v1.25.0
+	google.golang.org/genai v1.28.0
 )
 
 require (

docs/en/getting-started/quickstart/go/genAI/go.sum

@@ -102,8 +102,8 @@ golang.org/x/time v0.12.0 h1:ScB/8o8olJvc+CQPWrK3fPZNfh7qgwCrY0zJmoEQLSE=
 golang.org/x/time v0.12.0/go.mod h1:CDIdPxbZBQxdj6cxyCIdrNogrJKMJ7pr37NYpMcMDSg=
 google.golang.org/api v0.248.0 h1:hUotakSkcwGdYUqzCRc5yGYsg4wXxpkKlW5ryVqvC1Y=
 google.golang.org/api v0.248.0/go.mod h1:yAFUAF56Li7IuIQbTFoLwXTCI6XCFKueOlS7S9e4F9k=
-google.golang.org/genai v1.23.0 h1:0VkQPd1CVT5FbykwkWvnB7jq1d+PZFuVf0n57UyyOzs=
-google.golang.org/genai v1.23.0/go.mod h1:QPj5NGJw+3wEOHg+PrsWwJKvG6UC84ex5FR7qAYsN/M=
+google.golang.org/genai v1.28.0 h1:6qpUWFH3PkHPhxNnu3wjaCVJ6Jri1EIR7ks07f9IpIk=
+google.golang.org/genai v1.28.0/go.mod h1:7pAilaICJlQBonjKKJNhftDFv3SREhZcTe9F6nRcjbg=
 google.golang.org/genproto v0.0.0-20250603155806-513f23925822 h1:rHWScKit0gvAPuOnu87KpaYtjK5zBMLcULh7gxkCXu4=
 google.golang.org/genproto v0.0.0-20250603155806-513f23925822/go.mod h1:HubltRL7rMh0LfnQPkMH4NPDFEWp0jw3vixw7jEM53s=
 google.golang.org/genproto/googleapis/api v0.0.0-20250818200422-3122310a409c h1:AtEkQdl5b6zsybXcbz00j1LwNodDuH6hVifIaNqk7NQ=