[infra] Bump AGP to 8.6

Migrating to a version of AGP that supports API Level 35.

See https://developer.android.com/build/releases/past-releases/agp-8-6-0-release-notes

Author: rlazo

gradle/libs.versions.toml

@@ -3,7 +3,7 @@
 # it needs to match the protobuf version which grpc has transitive dependency on, which
 # needs to match the version of grpc that grpc-kotlin has a transitive dependency on.
 android-lint = "31.3.2"
-androidGradlePlugin = "8.3.2"
+androidGradlePlugin = "8.6.1"
 androidx-test-core="1.5.0"
 androidx-test-junit="1.1.5"
 androidx-test-truth = "1.6.0"