chore(deps): update dependency firebase/firebase-ios-sdk to from: "12.6.0" (#1923)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
|
[firebase/firebase-ios-sdk](https://redirect.github.com/firebase/firebase-ios-sdk)
| minor | `from: "12.5.0"` -> `from: "12.6.0"` |

---

### Release Notes

<details>
<summary>firebase/firebase-ios-sdk (firebase/firebase-ios-sdk)</summary>

###
[`v12.6.0`](https://redirect.github.com/firebase/firebase-ios-sdk/releases/tag/12.6.0):
Firebase Apple 12.6.0

[Compare
Source](https://redirect.github.com/firebase/firebase-ios-sdk/compare/12.5.0...12.6.0)

The Firebase Apple SDK (12.6.0) is now available. For more details, see
the [Firebase Apple SDK release
notes.](https://firebase.google.com/support/release-notes/ios#12.6.0)

To install this SDK, see [Add Firebase to your
project.](https://firebase.google.com/docs/ios/setup)

#### What's Changed

- \[Release] Update `Unreleased` changelog entries by
[@&#8203;andrewheard](https://redirect.github.com/andrewheard) in
[https://github.com/firebase/firebase-ios-sdk/pull/15436](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15436)
- \[Firebase AI] Fix Google AI `useLimitedUseAppCheckTokens` config by
[@&#8203;andrewheard](https://redirect.github.com/andrewheard) in
[https://github.com/firebase/firebase-ios-sdk/pull/15423](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15423)
- \[Firebase AI] Add internal JSON Schema support in `GenerationConfig`
by [@&#8203;andrewheard](https://redirect.github.com/andrewheard) in
[https://github.com/firebase/firebase-ios-sdk/pull/15404](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15404)
- Fix typos by [@&#8203;paulb777](https://redirect.github.com/paulb777)
in
[https://github.com/firebase/firebase-ios-sdk/pull/15445](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15445)
- Fix typo in SecureTokenService comment by
[@&#8203;gibachan](https://redirect.github.com/gibachan) in
[https://github.com/firebase/firebase-ios-sdk/pull/15448](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15448)
- \[Release] Update Carthage artifacts for 12.5.0 by
[@&#8203;andrewheard](https://redirect.github.com/andrewheard) in
[https://github.com/firebase/firebase-ios-sdk/pull/15452](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15452)
- \[Release] Update Carthage README for FirebaseAILogicBinary by
[@&#8203;andrewheard](https://redirect.github.com/andrewheard) in
[https://github.com/firebase/firebase-ios-sdk/pull/15453](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15453)
- \[Release] Update versions for 12.6.0 by
[@&#8203;andrewheard](https://redirect.github.com/andrewheard) in
[https://github.com/firebase/firebase-ios-sdk/pull/15458](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15458)
- remove func from codebase by
[@&#8203;themiswang](https://redirect.github.com/themiswang) in
[https://github.com/firebase/firebase-ios-sdk/pull/15456](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15456)
- \[AI] Server Prompt Templates by
[@&#8203;paulb777](https://redirect.github.com/paulb777) in
[https://github.com/firebase/firebase-ios-sdk/pull/15402](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15402)
- Prevent stale configuration data after iOS device restore by
[@&#8203;tusharkhandelwal8](https://redirect.github.com/tusharkhandelwal8)
in
[https://github.com/firebase/firebase-ios-sdk/pull/15442](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15442)

#### New Contributors

- [@&#8203;gibachan](https://redirect.github.com/gibachan) made their
first contribution in
[https://github.com/firebase/firebase-ios-sdk/pull/15448](https://redirect.github.com/firebase/firebase-ios-sdk/pull/15448)

**Full Changelog**:
firebase/firebase-ios-sdk@12.5.0...12.6.0

</details>

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Author: 3 people

examples/firebase_example/Package.resolved

@@ -7,7 +7,7 @@ let package = Package(
     dependencies: [
         .package(
             url: "https://github.com/firebase/firebase-ios-sdk",
-            .upToNextMajor(from: "12.5.0")
+            .upToNextMajor(from: "12.6.0")
         ),
         // Used by crashlytics example
         .package(