build: update build files

gradle/convention/src/main/kotlin/justjanne.android.app.gradle.kts

@@ -6,6 +6,7 @@ plugins {
   id("justjanne.kotlin.android")
 }
 
+@Suppress("UnstableApiUsage")
 android {
   compileSdk = 31
 

gradle/convention/src/main/kotlin/justjanne.android.library.gradle.kts

@@ -3,6 +3,7 @@ plugins {
   id("justjanne.kotlin.android")
 }
 
+@Suppress("UnstableApiUsage")
 android {
   compileSdk = 31