Update Kotlin and KSP to v2.0.21-1.0.25

[renovate]

Kotlin and KSP need to be updated together since each KSP version is tied to a Kotlin version. This PR will aggregate their updates. Once checks are passing because compatible versions are in use, this PR can be merged.

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.google.devtools.ksp (source)	2.0.20-1.0.25 -> 2.0.21-1.0.25
com.google.devtools.ksp:com.google.devtools.ksp.gradle.plugin (source)	2.0.20-1.0.25 -> 2.0.21-1.0.25

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Release Notes

google/ksp (com.google.devtools.ksp)

v2.0.21-1.0.25

Compare Source

What's Changed

• UPDATE_KOTLIN_VERSION: 2.0.21 by @​ting-yuan in https://github.com/google/ksp/pull/2145

Full Changelog: google/ksp@2.0.21-RC-1.0.25...2.0.21-1.0.25

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 17.82%. Comparing base (bcd93b3) to head (67bb6fa).
Report is 2 commits behind head on main.

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