Bump kotlin-stdlib-jdk8 from 1.6.10 to 1.6.21

Bumps [kotlin-stdlib-jdk8](https://github.com/JetBrains/kotlin) from 1.6.10 to 1.6.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.6.21/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/compare/v1.6.10...v1.6.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

uhabits-android/build.gradle.kts

@@ -87,7 +87,7 @@ android {
 
 dependencies {
     val daggerVersion = "2.41"
-    val kotlinVersion = "1.6.10"
+    val kotlinVersion = "1.6.21"
     val kxCoroutinesVersion = "1.6.1"
     val ktorVersion = "1.6.8"
     val espressoVersion = "3.4.0"

uhabits-server/build.gradle.kts

@@ -34,7 +34,7 @@ application {
 
 dependencies {
     val ktorVersion = "1.6.8"
-    val kotlinVersion = "1.6.10"
+    val kotlinVersion = "1.6.21"
     val logbackVersion = "1.2.11"
     implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlinVersion")
     implementation("io.ktor:ktor-server-netty:$ktorVersion")