Bump org.jetbrains.kotlin:kotlin-compiler-embeddable

Bumps [org.jetbrains.kotlin:kotlin-compiler-embeddable](https://github.com/JetBrains/kotlin) from 1.9.20 to 1.9.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.20...v1.9.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-compiler-embeddable
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

compiler-plugin/build.gradle.kts

@@ -30,7 +30,7 @@ val autoService = "1.0.1"
 dependencies {
     compileOnly("com.google.auto.service:auto-service:$autoService")
     kapt("com.google.auto.service:auto-service:$autoService")
-    compileOnly("org.jetbrains.kotlin:kotlin-compiler-embeddable:1.9.20")
+    compileOnly("org.jetbrains.kotlin:kotlin-compiler-embeddable:1.9.21")
     testImplementation("dev.zacsweers.kctfork:core:0.4.0")
     testImplementation("junit:junit:4.13.2")
     testImplementation("com.google.truth:truth:1.1.5")