build: mirror Maven Central for dependency resolution

The CI runner's egress IP is rate-limited by repo.maven.apache.org (HTTP 429 on a Robolectric native runtime jar), and a missing Gradle cache then breaks the run. Try Google's Maven Central mirror first and fall back to the canonical repository.

settings.gradle.kts

@@ -7,6 +7,9 @@ pluginManagement {
                 includeGroupByRegex("androidx.*")
             }
         }
+        maven("https://maven-central.storage-download.googleapis.com/maven2/") {
+            name = "MavenCentralMirror"
+        }
         mavenCentral()
         gradlePluginPortal()
     }
@@ -16,6 +19,9 @@ dependencyResolutionManagement {
     repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
     repositories {
         google()
+        maven("https://maven-central.storage-download.googleapis.com/maven2/") {
+            name = "MavenCentralMirror"
+        }
         mavenCentral()
     }
 }