Bump com.android.billingclient:billing-ktx from 5.2.0 to 6.0.0

Bumps com.android.billingclient:billing-ktx from 5.2.0 to 6.0.0.

---
updated-dependencies:
- dependency-name: com.android.billingclient:billing-ktx
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

lib/build.gradle.kts

@@ -67,7 +67,7 @@ dependencies {
 
     api("androidx.startup:startup-runtime:1.1.1")
 
-    val billingVersion = "5.2.0"
+    val billingVersion = "6.0.0"
     api("com.android.billingclient:billing-ktx:$billingVersion")
 
     implementation("androidx.annotation:annotation:1.6.0")