Update dependency org.jetbrains.kotlinx:kotlinx-serialization-json to v1.8.1

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.jetbrains.kotlinx:kotlinx-serialization-json	1.7.3 -> 1.8.1

---

Warning

Some dependencies could not be looked up. Check the Dependency Dashboard for more information.

---

Release Notes

Kotlin/kotlinx.serialization (org.jetbrains.kotlinx:kotlinx-serialization-json)

v1.8.1

==================

This release updates Kotlin version to 2.1.20, while also providing several important improvements
and bugfixes.

Improvements

• Implemented encoding null in key and value of a map in Protobuf (#​2910)
• Make type argument in JsonTransformingSerializer nullable (#​2911)
• Use SPDX identifier in POMs (#​2936) (thanks to Leon Linhart)
• Add watchosDeviceArm64 to Okio integration module (#​2920) (thanks to Daniel Santiago)
• Update kotlinx-io version to 0.6.0 (#​2933) (thanks to Piotr Krzemiński)

Bugfixes

• Fix incorrect enum coercion during deserialization from JsonElement (#​2962)
• Supply proper equals(), hashCode(), and toString() for SerialDescriptor() wrapper (#​2942)
• Do not encode empty packed collections in protobuf (#​2907)

v1.8.0

==================

This release contains all of the changes from 1.8.0-RC. Kotlin 2.1.0 is used as a default, while upcoming 2.1.10 is also supported.
Also added small bugfixes, including speedup of ProtoWireType.from (#​2879).

---

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 is behind base branch, or you tick the rebase/retry checkbox.

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

---

• If you want to rebase/retry this PR, check this box

---

This PR was generated by Mend Renovate. View the repository job log.